Their intended fifth victim was a 16-year-old girl whose name was never released to the public. She into a grocery store on November 10, 1986, naked and crying. When police got there she told them she had been abducted at knifepoint by a couple who then chained her to a bed in their house. She had been dragged into a car by them while she was walking in the suburbs alone. The woman stood by and watched as the man raped her repeatedly. The couple reportedly spoke about the possibility of injecting cocaine into David's penis to heighten his experience. The next morning, Catherine made the girl call her parents and tell them she had spent the night at a friend's house and was okay. The woman then took her back to the bedroom, but left her unsecured to go answer the door for a cocaine dealer. The girl then took off running out a window. She was able to give authorities the address and phone number of the couple who had kept her captive.
Perhaps this seems unnecessarily sloppy to some of you. Fortunately for this latest victim, the manner of Denise Brown's death had so disturbed Catherine Birnie that she had come to the end of her rope. This is perhaps what prompted her to leave their fifth intended victim alone and unrestrained. She had begun to believe the killing would never end and decided to give this victim a fighting chance. When she did, in fact, manage to escape, Catherine's only thought was to how angry David would be with her and whether or not she would be able to come up with a sufficient excuse to placate him.
With the victim free and police at the front door, Catherine admitted knowing the girl but refused to say more without her husband present. David claimed the girl had willingly come home with them to use some drugs and that all sex had been consensual. The couple was detained and confessed readily to the four other murders.
At trial, David pleaded guilty to four counts of murder and one count of abduction and rape. When asked why he did this so readily, he looked toward the victims' families and said, "It's the least I could do." Catherine's competency test found her sane enough to stand trial where she was sentenced to a life term in prison. After their incarceration, they traded over 2,600 letters between each other in their first four years apart, as it was their only form of contact.
On October 5, 2005, David Birnie was found hanged in his cell. Catherine continues to serve her sentence with little hope of gaining parole.