Officer Stone approaches the dimly lit motel he's been called to investigate.
Outside the shattered windows and broken door, the motel manager tells him the room was rented to Frank Carter, who was last seen entering the motel three nights earlier.
While Carter doesn't have the cleanest record, he's never been arrested for a violent crime before.
Yet as Stone scans the crime scene, he sees a disorderly room, visible red-brown stains and a partial shoe track.
All these details hint at a bloody struggle.
But there aren't enough clues to say exactly what happened.
After calling in a detective and a crime scene investigation team to inspect photograph, sketch measure and collect all the obvious evidence, the investigators decide their next move.
It's time to apply Luminol.
Luminol, also known as 3-aminothalhydrazide, was first introduced as an investigative tool in 1937 by a German forensic scientist named Dr Walter Specht.
Almost a decade earlier research found that when mixed in a solution with an oxidizing agent and exposed to certain compounds, luminol molecules rapidly oxidize, become excited and emit a faint blue-white glow as they return to their normal state.
This process is called chemiluminescence and Specht discovered he could trigger it by exposing the luminal to hemoglobin, a protein found in red blood cells.
So by spraying the solution in a dark crime scene, he could illuminate even the faintest traces of blood.
This is what Officer Stone is hoping to do back at the motel.
The lights are switched off and the forensic team sprays luminol across the walls, floor and ceiling.
The chemiluminescence only lasts about 30 seconds, so our investigators need to keep spraying as they track blood through the crime scene.
But if they find a trail, the specific patterns of blood could help reconstruct what might have happened.
In some crime scenes, luminol might reveal footprints or drag marks.
It can show larger drips associated with slowly bleeding wounds or fine spatter, suggesting high-impact wounds from firearms or motorized tools.
The absence of a reaction can be just as informative, indicating when people or objects blocked blood from hitting a surface.
And since luminol will react even if the blood is extremely diluted, it's almost impossible to clean a bloody crime scene well enough to prevent camilluminescence.
In fact, a skilled investigator can even use these lingering patterns to identify attempts at blood removal.
In this case, Officer Stone finds spattered spots of blue light on the floor, suggesting an impact wound and a struggle.
Shoe track impressions and a glowing handprint on the kitchen countertop line up with the drag mark on the floor.
Following the trail from the foot of the bed, the investigators end up in the parking lot, suggesting the victim was placed inside a vehicle.
These stains make a strong case for the narrative revealed by Luminol.
But investigators have to be careful, since the chemical's high sensitivity is a double-edged sword.
Not only does luminol react to very old bloodstains, with some cases showing chemiluminescence on objects thousands of years old, it can also react to cleaning agents like bleach or materials containing copper.
This is why Luminol is what's called a presumptive blood test.
It indicates the possible presence of blood.
But a confirmatory test with chemicals that only react to hemoglobin must be done to prove it.
If a positive reaction for blood is confirmed.
However, DNA tests can be especially useful for identifying and eliminating potential suspects.
Officer Stone submitted a DNA sample from the motel for that exact purpose, and the results found exactly the clue he needs.
The blood belongs to Frank Carter, suggesting that he may be the victim, not the culprit.
Stone is mulling over this new evidence when he gets a call from a local state trooper.
After pulling over an erratic driver, the trooper noticed what appeared to be blood stains on the rear bumper.
The car's trunk was empty, but luminol testing later revealed traces of blood throughout the car.
One more DNA test confirms Stone's suspicions.
Carter was the victim.
And faced with this overwhelming evidence, the car's driver confessed to the crime for 30 days free and 20 off a yearly subscription.
