The case continues to baffle investigators. Police don't believe anything was taken and to this day they don't know the motive for the horrific crime.
Forensic Pathologist Dr. Cyril Wecht performed the autopsy. He told Target 11 Investigator Rick Earle that he's done thousands of autopsies and this is one of the most brutal he's ever seen.
Stephanie Coyle was found on the floor or her bedroom in her Arnold apartment in July of 1993. After she failed to show for her volunteer job, her landlord went to check on her and discovered her body.
"This is truly one of the most brutal killings I've ever experienced in my role as a forensic pathologist," Wecht said.
On the victim's back, Wecht discovered a strange carving that he suspects was done with a knife after Coyle had been killed.
"It suggests some kind of symbol. This was the final message. It could even be some kind of initiation ritual," said Wecht.
Investigators won't release any photos of the carving, but according to Wecht it was an oval about 21 inches by 14 inches with a vertical line 25 inches long through the middle of the circle. The carving was about a quarter inch deep.
"It's still hard to believe that somebody can do that to anybody..., and here it is my own mother," said Dan Coyle, the victim's son.
Dan Coyle told Target 11 that his mother was retired and widowed. She spent her days volunteering at the New Kensington Senior Citizens Center. During the night she enjoyed bowling or bingo.
"We went through our minds hundreds of times. Just trying to see if she has any enemies. We couldn't come up with anyone. The big question is why? We still don't have than answer after all these years," Dan Coyle said.
"I always said when I started working in 1981 that I'd never let the job become personal. This is personal," said Arnold Police Officer Willie Weber, who is the lead investigator in the case.
Weber was one of the first police officers to responded to the scene in 1993.
"There were items in the house that a normal burglar would have taken. There was no ransacking of the apartment whatsoever. There wasn't a fight. It looked like she kind of surrendered and said do what you want to do, leave me alone and get out of here," said Weber.
Weber opened up the case file for Target 11 and revealed photos taken of the apartment the day of the crime.
Over the years, Weber has interviewed dozens of people, including some who were attending a nearby party. At one point, Weber said he thought he had a solid suspect, but it didn't pan out.
Weber said the victim's DNA has been entered into the national database, but there have been no matches.
As for that symbol carved on her back, Weber said that even FBI profilers who examined photos of the marking and reviewed the case file had trouble making sense of it.
"We have not been able to characterize it to any one group," Weber said.
Wecht also said there's a possibility that the killer was startled and never finished the message.
Investigators also said there's the possibility that the killer may have been trying to throw off investigators by making it look like something it was not.
Even after all these years, Coyle's son hasn't given up hope that the crime will one day be solved and the killer brought to justice.
Every year on the date of his mother's death, he posts flyers around Arnold, offering a $10,000 reward for information that leads to an arrest.
"I'm trying to keep people not forgetting about it. We just need that one tip. It's never ever going to go away but it would definitely help if it was solved," said Dan Coyle.
Anyone with information in the case is asked to call the Arnold Police Department at 724-339-9663.