David Muir

Both of these brutal murders were cold cases for decades. What links both of those cases all of these years later is the cutting-edge forensic technology inside this lab. Tonight, you'll see it unfold right here as they unmask the killer in both cases. It's the first week of December 1988. Nineteen-year-old Kathy Swartz is home with her nine-month-old daughter.

In Kathy's living room, a tree decorated, ready for the first Christmas for her little baby.

In Kathy's living room, a tree decorated, ready for the first Christmas for her little baby.

This is that baby left standing alone in that crib all those years ago. She's now 36 years old. How was your mother described to you?

This is that baby left standing alone in that crib all those years ago. She's now 36 years old. How was your mother described to you?

So detectives had questioned at the time whether or not this suspect had changed the diaper.

So detectives had questioned at the time whether or not this suspect had changed the diaper.

But when crime scene investigators pass through that gruesome scene again, this time with a new forensic light source, they find a new clue and one that was imperceptible to the naked eye.

But when crime scene investigators pass through that gruesome scene again, this time with a new forensic light source, they find a new clue and one that was imperceptible to the naked eye.

South Lanes is a bowling alley in Three Rivers, Michigan. It's the social epicenter of this small town where Kathy Swartz's father ran the pro shop. After her brutal murder back in 1988, it also became a place that connected Kathy's daughter, Courtney, to her mother.

South Lanes is a bowling alley in Three Rivers, Michigan. It's the social epicenter of this small town where Kathy Swartz's father ran the pro shop. After her brutal murder back in 1988, it also became a place that connected Kathy's daughter, Courtney, to her mother.

Your mother's best friend, Jennifer, has told you a lot about your mom.

Your mother's best friend, Jennifer, has told you a lot about your mom.

They were a young family just starting out. Kathy and Mike Warner had only been engaged about three weeks before her brutal death. And since he was the one who found her body, you know, of course, police would have a lot of questions for him.

They were a young family just starting out. Kathy and Mike Warner had only been engaged about three weeks before her brutal death. And since he was the one who found her body, you know, of course, police would have a lot of questions for him.

And when detectives speak to Kathy's friends, they hear about an ex-boyfriend named Troy Schultes. It turns out he had a nickname, Harley, which of course got their attention. He was a huge fan of the band Metallica.

And when detectives speak to Kathy's friends, they hear about an ex-boyfriend named Troy Schultes. It turns out he had a nickname, Harley, which of course got their attention. He was a huge fan of the band Metallica.

And he said, well, I didn't do it. And still with no solid alibi for the night of the murder, police zero in on Troy.

And he said, well, I didn't do it. And still with no solid alibi for the night of the murder, police zero in on Troy.

And before long, an arrest in the Kathy Swartz case is announced. But if investigators think they've got their guy, a rude awakening is ahead. Kathy Swartz's daughter Courtney, the baby left standing in her crib after her mother was brutally murdered, is a mother herself now.