Tonight on Dateline.
She was really looking forward to creating her own family.
We tried our best.
And sorry it wasn't enough.
Because if it was, she would be here.
They found Sandra deceased in her apartment.
I was told that she had committed suicide.
But in the back of my mind, it isn't adding up.
Given how excited she was about becoming a mom, it didn't jive with us.
This broken necklace, this was a clue to you?
Definitely, yeah.
I said, that sounds like a sign of a struggle.
When I first saw the video, my jaw dropped.
He's walking into the apartment.
He has a mask on.
He's got a hoodie on over his head.
I'm thinking somebody murdered her.
You're thinking cover up?
Definitely.
Your investigation revealed a bombshell.
Yes, it did.
Wherever that led us, we would go.
A young mother-to-be murdered.
Who was behind it?
A twisted mystery that would stun even the police.
I'm Lester Holt and this is Dateline.
Here's Andrea Canning with The Betrayal of Sandra Birchmore.
It was a cold, blustery start to the week that February 1st, 2021.
It is hammering snow.
We're up to, I think, three inches per hour.
The temperature was dropping.
The winds were howling.
A nor'easter is coming into town.
Yes.
And as we all know, that can affect schools and children.
Correct.
Yep.
So we had to leave school early on a Monday afternoon.
Cheryl Carlson, then assistant principal at East Elementary School just outside of Boston, scrambled to get everyone out the door before the storm hit.
There was a lot going on when we have to be calling parents, making sure students are getting home.
23-year-old teacher's assistant Sandra Birchmore was helping out.
How is she on this day?
She seemed fine.
Didn't have any big conversation with her, but there was nothing that struck me as different.
But when school reopened three days later, Sandra wasn't in her classroom.
I get a call asking, have I seen Sandra?
And no, I haven't seen her yet that day.
I'm like, is she not here?
Like, no, she hasn't shown up.
Are you worried about her?
My mind didn't immediately go to super worried.
Cheryl thought there might be a simple explanation that Sandra wasn't feeling well or forgot to mention an appointment, something going on that she didn't communicate about.
One of the secretaries kept trying to call her.
I think it went straight to voicemail.
That's always worrying.
It is what do you do?
What how do you?
Yeah, the school contacted this, the school resource officer that we worked with.
That school resource officer then tried to get the ball rolling.
The first call was to the police department in the town of stoughton, where school records showed sandra lived.
So we were notified and asked to do a well-being check.
Donna McNamara is the Stoughton chief of police and immediately recognized her name.
You knew her?
Yes, I did.
She was part of the Explorer program.
I would see her within the police station.
As a teenager, Sandra had been part of the department's program which exposed kids to different careers in law enforcement.
Now, officers learned she had recently moved to nearby Canton, so that department took over.
So Canton police goes over then?
Yeah, the Canton police and I believe the school resource officer in Canton also had gone over.
Officers knocked on her door with no answer.
They reported back to the station.
Sandra's blue Chevy was there.
So officers asked the building manager for a key to her apartment.
So the two officers walk in.
They later note that they walked through a kitchen that was very untidy, that there were bills stacked up.
Journalist Michelle McPhee covered Sandra's story for Boston Magazine.
There was no sign of a struggle.
There was no sign of a break-in.
There was also no sign of Sandra.
And then they make their way into a bedroom where there is this young woman.
She has the strap of a duffel bag wrapped around her neck.
An officer noted in his report that Sandra had hanged herself.
To the responding officers, this just looked like somebody who had taken their own life.
Police notified Sandra's aunt...
Word traveled fast among the rest of her family.
That is such a shock to the system.
Sandra's cousin, Barbara Wright, says none of it made sense.
She texted with Sandra the night of the storm.
She seemed fine.
Were you ever worried about her?
No.
That she would take her own life, that she would do something drastic.
No.
I think if she felt that way, she would let me know.
She would reach out to me.
I knew she wouldn't do that.
I just knew it.
Another of Sandra's cousins, Justina, agreed.
I said, nope, didn't happen.
Why were you so sure?
Because like, I had just seen her and she was so happy and you know, like the tracks of her life were on track, you know.
It must have just sent chills down your spine when you hear something like that.
Absolutely.
Absolutely.
Sandra's boss couldn't shake the feeling that there was more to her death.
It didn't add up at all.
It was actually really scary to hear that.
What do you mean by scary?
It was scary to hear that news. that could she actually do that?
Or did this, did somebody have a part in this?
Wow.
You thought that?
Yeah.
Like, immediately?
Yeah, pretty much.
That is scary when you start to think that this could be murder.
Yeah.
And so I was like, did somebody force her to take pills?
What was it that happened?
Just doesn't make sense.
But if she didn't take her own life, who would want her dead?
Sandra's family remembered a recent conversation.
We were at breakfast with her and really kind of drilling it down and saying, what's his name?
Where does he work?
The quest to uncover the truth had only just begun.
They dehumanized her in their text messaging, in their interactions.
It's vile.
This is a person who had power, and this is a person who might get away with it.
Sandra had a lot of secrets.
She did.
She kept them well, too.
23-year-old Sandra Birchmore's body had been taken to the chief medical examiner's office for an autopsy.
Investigators believe she'd taken her own life, but it was hard for her many cousins to fathom.
They say Sandra, an only child raised by a single mom and working-class Stoughton always seemed full of life.
She was very rambunctious, very energetic, feisty.
And outgoing says cousin Angelique Perozzi, she was smart and she was interested in other people and she wasn't, you know, shy.
Cousin Antonetta remembers how close Sandra was to her mom, Denise.
They always did things together.
Her mother always had the best interests, you know, for Sandra.
But Denise was not well.
She had asthma, she had heart disease, she had diabetes.
She wasn't well for a good portion of Sandra's life.
Oh man, that's hard.
The family says, with Sandra's father not in the picture, her mom looked for strong role models for her daughter.
Martial arts instructor Michael Varner was one of them.
Sandra joined his gym when she was around 11.
And how did she take to it, Sandra?
How did she do?
I mean, she had a blast.
She always had a smile on her face.
Sandra's mother hoped the Stoughton Police Explorers Program would also be a safe place for her to thrive.
She enrolled Sandra when she was 13.
It was modeled after a nationwide program that had been around for decades and was created by the Boy Scouts of America.
The curriculum was hands-on.
Law enforcement officers taught classes, led boot camp drills, and arranged ride-alongs.
So your gym is literally right across the street from the police department.
Yep, right here.
Stoughton Police.
And so you would see the young explorers out here?
I would, yeah.
They would be right here in the parking lot.
Would you ever see Sandra out here?
Yeah, yeah.
Did she seem into it?
Oh, yeah.
She loved it.
Chief McNamara was a lieutenant back then.
So I would imagine that it could set a kid straight or it could inspire a child to want a career in law enforcement.
So that was the goal of the program, gives them a little discipline.
Something Sandra may have needed.
The chief says her teen years were rocky at times.
I had been on a couple calls, responded to calls to her home when she was a young teenager, with her mom.
She's fighting with her mom?
Yes.
Would it get physical?
No.
Sometimes it was just not seeing eye to eye growing up.
Sandra stayed with the Explorers through high school.
She talked about becoming a police officer or joining the military.
Then her world collapsed.
Her mother passed, and then a month later, her grandmother died.
The poor girl.
I know.
Sandra pushed forward and got an associate's degree in criminal justice, but eventually gave up on her dream of wearing a uniform.
She suffered from asthma and at only 4'10", didn't think she'd meet the physical requirements.
So Sandra became a teacher's assistant while she prepared for her new goal, nursing school.
She had a caring side of her.
She cared about people so much.
Then, in December 2020, less than two months before she died, Sandra made a big announcement.
She came in like kind of bouncing into the building, right into my office, and said I just want you to know I'm pregnant.
She told me yes, that this was great news.
She had been trying to get pregnant.
Cheryl says Sandra was an oversharer.
She was used to her revealing personal details.
Basically that her boyfriend, who was currently in a relationship with children.
The plan was that he was going to leave that relationship.
She's telling you all this in this baby announcement meeting?
Yes.
I mean, is your head spinning?
A little bit.
Sandra also shared the news with Barbara, but wouldn't tell her the name of the father.
Did you say to her, why don't you tell me who it is?
I didn't want to push at the time.
I knew that she was reluctant to talk, but I knew that eventually she would tell me.
Justina and Antonetta, who asked that their last names not be used, met with Sandra at a restaurant a week before she died.
She told them she was about two months along in her pregnancy and revealed something troubling.
She proceeded to tell us that the father of the baby was married.
She had also told us that his wife was also pregnant.
That's a lot.
What advice do you have for her hearing all of this?
I said, Sandra, you realize that you're probably raising this child on your own.
To the cousins, it sounded like the worst possible scenario.
We were really kind of drilling it down and saying, what's his name?
Where does he work?
She ended up telling us his name was Matthew.
Did she give you a last name or do you need to search that on your own?
No, she did not give us a last name.
She did share her expectations of Matthew as a father.
I felt like she had so much hope that he was going to be involved in the baby's life and he was going to put his name on the birth certificate.
And I just thought inside my head, like, that's never going to happen.
How did you leave... that breakfast feeling about everything you just heard?
I'm worried.
I remember thinking to myself, this might not end well.
Now, after Sandra's death, her family had questions.
Did her married boyfriend have something to do with it?
My gut was telling me that her pregnancy was a ticking time bomb for him.
Chief McNamara knew Sandra had gone through some tough times.
I think growing, you know having a difficult life growing up.
She had some issues with regards to her mental health.
So when she heard Sandra had taken her own life, she wasn't completely surprised.
Just eight months earlier, Stoughton Police had responded to an incident.
She had a family member that was concerned for her well-being.
So possibly threatening to take her own life?
Yes.
Officers took Sandra to a hospital where doctors evaluated her and determined she was not a risk to herself.
Barbara says Sandra insisted she wasn't suicidal.
She had threatened to harm herself in the heat of an argument, not out of despair.
Barbara believed her.
Depression and anxiety runs in the family, so.
So she was working on that.
She was doing well.
Yeah.
She was going to therapy every week.
I don't know how often.
And she was on medication.
Sandra's boss, Cheryl, also knew she was talking to someone.
After Sandra's death, she reached out to the therapist to let her know what had happened.
Her therapist was in shock.
She said that she had just seen Sandra on Friday afternoon, and everything seemed fine.
Is the therapist in agreement with you that this does feel odd?
She was.
We didn't talk about what that really meant, but she did say that it just didn't add up.
Cheryl told investigators what the therapist said.
She also shared her own doubts about whether Sandra had ended her life.
But Angelique, she wasn't sure what to believe.
I was very open to the idea that this was possibly a suicide.
But I was equally as open to the idea that this wasn't.
She wanted to make sure investigators weren't missing anything, especially the alarming information Sandra had recently shared about her boyfriend, Matthew.
Sandra didn't reveal his last name, but told her cousins that not only was he married with kids, he was also a police officer.
And not just any police officer.
He worked for Stoughton PD, the very same department that ran the Explorers program and had been such a big part of Sandra's life from ages 13 through 18.
A quick look online revealed who he was.
Longtime police officer.
Yeah.
What was his name?
Matthew Farwell.
Farwell was a detective and had been with the department for nearly a decade.
Angelique reached out to the state police detective unit in the Norfolk County District Attorney's Office.
They had taken over the case.
I called them cold, didn't have a name, asked for whoever was in charge of the investigation.
She got through to Sergeant John Fanning, the lead investigator.
Angelique says she told him everything.
Did the state investigator you spoke to know about this relationship by the time you two talked?
If he did, he didn't say it.
She says Sergeant Fanning listened carefully but disclosed very little.
So after the call, she turned to social media.
I posted on Sandra's Facebook page and said if you know anything, here's who to call and here's his phone number.
Angelique says she got plenty of responses and they all had one thing in common.
I couldn't find anyone in Sandra's life that thought she was suicidal.
Not only that, Sandra's cousins knew she was excited for the future.
She'd had an ultrasound, called a baby photographer, and was planning a big reveal on Facebook.
She was going to announce the pregnancy on Valentine's Day.
In their minds, the answer was clear.
Sandra's death was the result of foul play, and Matthew Farwell was somehow involved.
Angelique was now convinced as well.
My gut was telling me that her pregnancy was a ticking time bomb for him.
The state police interviewed Farwell in a school parking lot just two days after Sandra's body was found.
Journalist Michelle McPhee.
During this interview, Farwell freely admits that he had had sex with Sandra Birchmore.
Farwell acknowledged that he met Sandra in the Explorers program when she was a teen, but said their affair didn't start until she was 22 and lasted less than a year.
He explained that by saying, in 2020, I got drunk one night.
I had an affair with her.
I slept with her two or three times.
The last time I slept with her was October in 2020.
Two months later, Sandra told him she was pregnant and said he was the father.
But Farwell insisted the timeline didn't match up.
Essentially, Matthew Farwell denied being the father of the child.
He suggested that she was a problematic person who was sleeping around.
He said the last time he saw Sandra was the night of the Nor'easter.
Farwell said that he went by the house to break it all off.
An argument had ensued.
He said, I'm not the father of this child.
Some words were exchanged, and then he left.
When Angelique heard what Farwell said, she didn't buy a word of it.
Her cousin, the oversharer, would have told someone.
If the love of her life came to her house and broke up with her, You bet there would have been lots of phone calls and lots of text messages from Sandra to her loved ones to talk about it.
But the fact of the matter is, is no one heard from her again.
Angelique's suspicions about Farwell were deepening.
So were Barbara's, especially after she learned.
Other relatives found something odd while cleaning out Sandra's apartment.
They found a broken necklace, her broken flamingo necklace that she used to wear all the time.
And I said, well, that sounds like a sign of a struggle.
The family gave the necklace to the state police.
In the meantime, Angelique called the medical examiner's office and spoke with one of their investigators.
They said there was no signs of broken bones or the body being battered or bruised.
Weeks later, Angelique got an update from investigators.
They'd requested a second interview with Detective Farwell, as well as a DNA sample.
His attorney declined on his behalf.
It seemed state police might be onto something.
But three months after Sandra's death, the investigation came to a standstill when the medical examiner's office officially ruled it a suicide.
Sandra's cousins refused to accept it.
If she didn't take her own life, her killer's out there.
And her killer is possibly on the police force.
Yeah, exactly.
You know, this is a person who had power, and this is a person who might get away with it.
Chief McNamara was also concerned.
Farwell was one of her officers.
So she leapt into action with an investigation of her own.
Your internal affairs investigation revealed a bombshell about what else was going on in Sandra Birchmore's life.
Yes, it did.
With Sandra Birchmore's death ruled a suicide.
Her family feared the state police had ended their investigation.
It was close as far as I knew.
It was upsetting, very upsetting.
Because you probably must have felt so helpless.
I did.
It's almost like Sandra Birchmore was forgotten about.
There's no headlines.
There's no real probe of, hold on a minute, but what about that guy Matthew Farwell?
It was a question that had plagued Chief McNamara.
And whether Sandra took her own life or not, she believed she had to do something.
She'd worked with Farwell for years and watched Sandra grow up.
It was very concerning to me that he was admitted to having a sexual relationship with her.
And while she had no jurisdiction over Sandra's death because she died in Canton, McNamara could look into Farwell's conduct as one of her officers.
When the state police let her know Farwell was having an affair with Sandra, she launched an internal affairs investigation and soon placed him on paid administrative leave.
He's not doing anything, though.
He's not allowed to do anything, no.
McNamara put her deputy chief in charge of the probe and hired private investigators.
They caught a break after learning the state police had gathered data from Farwell's phone and Sandra's phone and laptop.
That's when they started to turn over what they could to us as far as the text messaging.
McNamara's team couldn't believe what they were seeing.
Tens of thousands of text messages between the two.
For more than a year they sorted through the texts, combed through Sandra's social media accounts and conducted interviews.
We discovered that on multiple occasions, Matthew was on duty when he was having sex with Sandra.
But that was just the beginning.
McNamara's investigators uncovered unimaginable secrets in those messages, including evidence of a sexual relationship between Sandra and another Stoughton officer, Matthew's twin brother, William Farwell.
There was text messages asking her to take pictures of herself and video herself.
It was pretty sick.
The twins are sharing Sandra sexually.
Yes, that's very, very sickening.
Amazingly, it doesn't end there.
No, the horror continued, unfortunately.
Chief McNamara says there were also Facebook messages they believed were written by a third Stoughton police officer.
Officer Robert Devine.
The messages discussed meeting Sandra for sex.
Devine ran the Stoughton Explorers program for more than a decade, and the Farwell brothers were his instructors.
All three met Sandra in the program when she was a teenager.
It's just horrific to find this information about people that are supposed to be protecting others.
They dehumanized her in their text messaging, in their interactions, and it's vile.
But McNamara says the most disturbing revelation of all was that Matthew Farwell's sexual relationship with Sandra began when she was just 15.
He was 27.
There was text messages between Matthew and Sandra discussing Matthew and her having a relationship, a sexual relationship, prior to being 16.
That's a crime.
Yes, if Sandra was alive, there would be charges for statutory rape, aggravated statutory rape.
Would you describe Matthew Farwell as a predator?
After what we've discovered in our internal affairs investigation, I would say that there was a control.
He controlled her.
He was grooming her.
And it was abuse at the worst level.
Was your plan to fire him?
That was the plan, yes.
That didn't happen?
No.
When we wanted to interview him, he chose to resign.
Stoughton PD then informed Farwell's brother and Robert Devine they were also under investigation.
Months later, they voluntarily left the department.
Is there any evidence that William Farwell and Robert Devine had sexual relations with her when she was underage as well?
No, that was not discovered in our internal affairs investigation.
But the team wondered, was Sandra an isolated case or a part of something bigger?
The Stoughton Police Explorers Program disbanded the year after Sandra graduated from high school, so they tracked down former members.
Did you find any other instances of potential statutory rape within the Explorers Program?
No, we did not.
After 19 months, in 2022, the team completed its final report detailing its findings against the three former officers.
Then, Chief McNamara did something that sent shockwaves through Norfolk County.
She went public with a redacted version of it.
All three men, the Fawa brothers and Devine, violated their oaths of office and should never have the privilege of of serving any community as a police officer.
The Stoughton Police Department recommends, without delay, their certification to serve as police officers be permanently revoked.
This is big.
You've got it out there in the public now.
Why do that?
We had an obligation to report our findings to our community.
And I was not going to allow them to get away with what they had gotten away with.
While the chief's investigation did not explore how Sandra died, only her officers' on-duty conduct, by the end she'd come to suspect Sandra did not end her life and that Matthew Farwell was responsible.
It is something I've never had to deal with in my career before and so unusual and disturbing.
The Farwell brothers have never admitted to any wrongdoing but eventually agreed to a lifelong ban from law enforcement in Massachusetts.
Robert Devine is still fighting efforts to revoke his certification.
He denies all allegations and told investigators he didn't write those Facebook messages to Sandra.
His account had been hacked.
Through their attorneys, all declined a request for an interview.
For Sandra's family, the details of McNamara's report were heartbreaking.
It made me very sad for Sandra to be so used.
But would the explosive findings be enough to jumpstart a murder investigation?
It would take a high profile trial in the same county, along with a viral video, to shine a bright light on Sandra's death.
When I first saw the video, my jaw dropped.
Sandra's family had high hopes.
The Stoughton PD report would finally be enough to ignite a murder investigation.
But it went nowhere with the district attorney.
Angelique says the state police repeatedly told her there was no evidence that Matthew Farwell killed Sandra.
They were hanging their hat on the ME's report.
It was a suicide.
If they don't believe she was murdered, then none of what you're saying has any relevance.
Yes, exactly.
However, media coverage of Sandra's story was growing and a few reporters were starting to question the state police investigation.
Michelle McPhee was one of them.
Perhaps this woman didn't kill herself at all.
There were certainly a number of people who had motive to see her go away.
Boston-area podcasters Kirk Minahan and Dave Cullinane agreed.
They'd been looking into Sandra's death for their true crime podcast called The Case.
When Sandra Birchmore crossed our radar, It was too compelling a story to ignore.
And after months of pushing for access to evidence, Kirk and Day's efforts paid off when the DA's office turned over security footage from Sandra's apartment building.
You saw Sandra a few times in that during the day.
That's Sandra on the day of the Nor'easter, walking into her building carrying a snow brush.
She went to clean out her car.
It was a snowstorm that day.
Hours later, Matthew Farwell arrived, just as he had told the police.
It's one thing to hear that he had been over there, came and went, and it's a whole other thing to see it with your own eyes.
Farwell took the elevator to sandra's floor.
Then 29 minutes later, he came back down and exited the building.
The podcasters posted the security video on social media and recorded an episode about it.
After we saw matt leave, she didn't respond or send a message to anybody.
The video quickly went viral, with nearly 2 million views on TikTok.
When I first saw the video, I just, my jaw dropped.
It was chilling to see him get on the elevator.
One of the things that took me was just how big he was and how small Sandra was.
Remember, Sandra was only 4'10".
Farwell, 6'4".
I think the video raised questions that any average person curious about a crime would ask, but certainly it should have been taken a little bit more seriously by investigators.
While the podcast drew more attention to Sandra's story, Kirk and Dave say many of the people they'd spoken to were either too scared to speak out against law enforcement or unwilling to say anything on the record.
I don't think anybody will ever serve a day in prison for any of this.
I don't think that's going to happen.
Then in 2024, out of the blue, finally the call Sandra's family had been waiting for.
It was an FBI agent.
That's a good day.
It was a great day for the FBI to call you and say, we'd like to talk to you.
And I was like, wow, like now we're going to get somewhere.
Two agents came to her house and she told them everything she told the state police.
And they were very clear, look, you might not ever hear from us again.
Or, you know, it could be two years from now and then you'll hear from us.
But don't expect anything anytime soon.
You know, I took that to heart.
As the family waited, all eyes were on another case in the same county the high-profile murder trial of Karen Reed.
Opening statements in this highly anticipated case, it started earlier this morning.
Reid was accused of killing her boyfriend, Boston police officer John O'Keefe.
His body was found in Canton, the town where Sandra died.
The defense in Reid's case alleged state police botched the investigation and even planted evidence charges they denied.
Reid would ultimately be acquitted of the most serious charges after two trials.
What concerned Sandra's family, the same DA and law enforcement agencies were investigating Sandra's death.
You have to think about Karen Reed and what we all saw on TV there.
I think the whole state just started to pay attention to both cases, like what is actually happening here.
What is the state police doing?
Meanwhile, Sandra's aunt had filed a wrongful death lawsuit and hired prominent forensic pathologist, Dr Michael Bodden, to review Sandra's autopsy report.
The summer of 2024, his findings made headlines in the Boston Globe, concluding what the family had long believed.
Sandra's death was a homicide, not a suicide, and she'd been strangled.
This is a game changer when Dr. Michael Bodden comes on the scene.
Yes.
It changed everything.
And soon, the FBI would go public with its investigation, exposing devastating details that would crack the case wide open.
To me, that's almost the key moment in this entire thing.
That's pouring gasoline on this.
Absolutely.
August 28th 2024, just five months after Angelique got that call from the FBI, the agent reached out again with stunning news about Matthew Farwell.
She said that they had just arrested him.
And they were bringing him in to be arraigned.
What's going through your body, your mind in this moment?
I was shocked.
I was speechless.
I mean, I was sobbing by the time we hung up.
Three and a half years after Sandra Birchmore's death, the U.S.
Attorney's Office did what the Norfolk County D.A. had not.
It indicted Matthew Farwell for Sandra's murder.
I've never seen this happen before.
Nearly four years later, the FBI comes up with a completely different conclusion.
Does this come out of left field for you?
No, it wasn't something that came out of left field for me because I was assisting the FBI.
That's because two years earlier they'd reached out to the chief and asked her about her internal affairs probe.
I hope that what we uncovered in our investigation was a significant part in leading to that indictment.
Just hours after his arrest, Matthew Farwell was arraigned in a Boston federal court for strangling Sandra.
Prosecutors alleged he murdered Sandra to prevent her from disclosing his sexual exploitation of her while on duty.
Chief McNamara was there.
It's just disgusting that he was in this point in his life and he was in shackles and leg irons.
In a press conference, the U.S. attorney for Massachusetts laid bare the findings.
We allege that Sandra Burchmore survived years of grooming, statutory rape and then sexual violence, all at the hands of Matthew Farwell.
And he used his knowledge and experience as a law enforcement officer to stage her death to look like a suicide.
In a 45-page affidavit the FBI alleged Farwell groomed Sandra from an early age, paying extra attention to her outside the Explorers program.
Sandra told a relative she and Farwell would meet at the library so he could help her with her homework.
And when she was 15, he sent her a friend request on Facebook.
Six months later, they had sex for the first time.
Grooming is a pattern of, you know, building a relationship, of someone in a position of authority and trust.
And he held a position of authority as a police officer.
The FBI painted a picture of Farwell as a man who had quote an interest in violent sex and has a history of choking Sandra.
They said Farwell first introduced his fetish to her when she was around 16.
Texting I'll choke you.
I'll grab your throat.
But in the months before Sandra's death, the FBI alleged Farwell was losing control over her.
She threatened to expose their affair.
He was under increasing pressure.
His wife is pregnant.
Sandra Birchmore is telling everyone that her baby is his.
She wants him to put his name on the baby's birth certificate, which is a public record that he is the father of this child.
The affidavit included texts from Farwell that showed how angry he was about Sandra's pregnancy.
And in a call Sandra told one friend that Farwell quote wished she would just die and wants nothing to do with the baby.
This was threatening his marriage, his family, a mistress, a baby.
Right.
He built this world for himself, and it was collapsing.
Because now, finally, she was starting to say, I'm not putting up with this anymore.
I'm going to tell your wife.
I'm going to tell people in the police station.
Agents said Sandra didn't follow through on that threat.
But 12 days before she died, one of her friends called the Stoughton Police Department and revealed the affair.
The person who answered the phone went to Matt Farwell and told him.
And to me, that's almost the key moment in this entire thing.
That's pouring gasoline on this.
Absolutely.
Prosecutors allege that's when Farwell set his plan in motion to kill Sandra.
So I think the federal prosecutors made it very clear that they had overwhelming evidence that pointed to Matthew Farwell as a murderer.
Agents also confirmed that Sandra met with her therapist in the days before her death and showed no signs of being suicidal.
The prosecutors' theory?
The night of the Nor'easter, Farwell entered Sandra's apartment knowing he was going to end her life.
A forensic expert noted there was evidence consistent with blunt force trauma to Sandra's chest and that she'd been strangled.
The expert also believed that broken necklace Sandra's family found on her bedroom floor suggested there was a struggle, just as her cousin suspected.
The affidavit reads, quote, "...the necklace was broken and hanging from the left side of her neck.
It was visible in crime scene photos but was never mentioned in the police reports released to the public.
When you think that a clue like that is omitted?
It's unbelievable.
As was the timing of Sandra's death.
The government's affidavit alleged that less than 13 hours after Farwell killed Sandra and her unborn baby, his third child was born.
This is quite possibly one of the craziest parts of this story.
Right.
We have a picture of Matt Farwell wearing a mask, holding up his little baby the next morning.
I can't imagine what was going on in his head.
I don't know how he could have justified that in his mind at all.
And this summer, surprising news.
According to three sources familiar with the investigation, DNA testing showed that Matthew Farwell was not the father of Sandra's baby.
Farwell has pleaded not guilty and is in the custody of the U.S.
Marshals Service.
No trial date has been set.
His legal team says they are not permitted to comment, but a previous lawyer told Dateline.
I hope that you keep an open mind, and that's what viewers do too.
What is released publicly is not necessarily the full story.
That's what a jury trial is for.
The U.S.
Attorney's Office, the Massachusetts State Police and the Norfolk County District Attorney have declined to be interviewed.
The DA's office did issue this statement.
The Norfolk District Attorney's Office spent substantial time and effort investigating, interviewing and analyzing evidence in the tragic death of Sandra Birchmore.
The investigation remained open.
And their state police investigators have participated and worked collaboratively with the United States Attorney's Office.
The office of the chief medical examiner continues to stand by its ruling that Sandra's death was a suicide.
Birchmore were based on the evidence available at the time of determination.
Do you feel like the system failed Sandra Birchmore?
Yeah, I don't really know.
I mean, I don't know how to answer that.
But preliminary, from the outside, it does look that way.
Her death has ruled a suicide, which is now in question.
Why was it ruled so quickly?
When you put it all together, it is a failure in maybe many, many areas.
And we are hopefully working towards justice for her.
Sandra's family is committed to fighting to the very end.
Sandra, what would you like your final words to be about her?
And that she's not forgotten in all of this?
You know, we tried our best.
And sorry it wasn't enough.
Because if it was, she would be here. wasn't enough.
That's all for this edition of Dateline.
And don't forget to check out our Talking Dateline podcast, in which we'll go behind the scenes of tonight's episode, available Wednesday in the Dateline feed, wherever you get your podcasts.
We'll see you again next Friday for our two-hour season premiere at 9, 8 Central.
I'm Lester Holt.
For all of us at NBC News, good night.
