By Joe Holden

MARCUS HOOK, Pa. (CBS) — The murder of an 18-year-old Delaware County woman captured headlines in the early 1980s, but the case had gone cold — until now.

Denise Pierson never came home the night of April 14, 1981.

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The 18-year-old teen from Marcus Hook was last seen with a group of guys. Family, including Pierson’s mother, became deeply worried.

“She initially went with Peter Horn and others to Delaware with the purpose to purchase drugs,” Delaware County Assistant District Attorney Geoff Paine said.

Remember the name, Peter Horn.

Prosecutors would later conclude Horn was a co-conspirator in her murder.

Meanwhile, for Pierson, she wanted to get home.

Investigators say over the hours, Pierson developed a sixth sense, feeling she should no longer be with this group of guys. But for her, it was too late.

“She attempted to leave and was not allowed to leave,” Paine said. “She was physically restrained from leaving.”

Inside a home owned by Horn that was torn down years ago, Pierson was hit with an object and lost consciousness.

“She was tied up, placed in a wheelbarrow and taken to the railroad tracks,” Paine said. “She was then hit more times. A knife was used on her. She succumbed to those injuries.”

Pierson’s remains were left there for years, her family believing she was missing the entire time.

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“She had debris placed over her to somewhat hide her body,” Paine said.

Kids playing along the tracks in 1984 discovered bones.

Over the years, investigators made small strides in developing a case.

Horn was long front and center. Horn is now dead.

Other men were also in the shadows of the case, including Wayne Anthony Walker.

A recent forensic analysis of that knife found with Pierson’s remains was able to provide a huge break. Police say Walker was there when Pierson was fatally slashed.

“It placed him as also being part of when she was actually murdered at the train tracks,” Paine said.

District Attorney Jack Stollsteimer says Walker almost got away with murder, if not for the forensic scientist.

“She was able to take a look at the evidence and make a determination that this poor girl was still alive at the time she was taken to the train tracks,” Stollsteimer said, “where she was ultimately left to rot. Her body was literally left out there, they didn’t bury her. She stayed out there for three years before she was discovered.”

Walker was arrested earlier this month. It’s unclear if he’ll be competent to face court proceedings. But detectives are homing in on others.

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“There are two other individuals out there. We know who they are,” Paine said. “We are actively putting together evidence to try and charge them.”