Ep 9. Invisible Intruder

Invisible Intruder is an episode of Forensic Files season 3 that tells the story of Mary Morris, a Wisconsin woman who was found murdered in her own home in 1986. The investigation into her death would hinge on a single fingerprint found on a light switch in her bedroom.

When Mary didn't show up for work one day, her coworkers became worried and called the police to ask for a welfare check. When officers arrived at her house, they found the front door unlocked and Mary's body lying on her bed. It was immediately apparent that she had been sexually assaulted and strangled to death.

Detectives searched Mary's house for clues, but found only a few items missing, leading them to believe this was not a robbery gone wrong. Instead, they began to suspect that Mary knew her killer, and that the motive for her murder was personal.

The only piece of evidence that detectives had to go on was a single fingerprint found on a light switch in Mary's bedroom. This fingerprint was quickly sent to the state crime lab for analysis, where it was compared against the fingerprints of known suspects.

Meanwhile, detectives conducted interviews with Mary's friends and family, hoping to uncover new leads. One friend told detectives about a man who had befriended Mary a few weeks before her death, and had even helped her move some furniture into her new house. This man's name was Christopher O'Kroley.

As detectives started to look into O'Kroley's past, they found that he had a violent criminal history, including a conviction for sexual assault. They also discovered that a few days before Mary's murder, O'Kroley had been involved in a bar fight where he had broken his hand.

This injury would turn out to be a crucial piece of evidence in the case. When O'Kroley was taken into custody for questioning, detectives noticed that his broken hand was still swollen and tender. They took pictures of his hand and compared them to the pattern of bruising found on Mary's body. The two matched perfectly.

After being confronted with this evidence, O'Kroley confessed to the murder. He admitted that he had broken into Mary's house, sexually assaulted her, and then strangled her to death. He had even come back to the house the next day to try and clean up the evidence, but had missed the light switch where his fingerprint was found.

Thanks to the tireless work of detectives and the precision of forensic science, Mary's killer was brought to justice. The fingerprint that had been the key to solving the case was a true example of the power of forensics in identifying and bringing to justice those who seek to harm others.