Oklahoma authorities hope a key ring unlocks a decades old mystery and solves the cold case murder of a college student viciously stabbed to death on her 21st birthday.

The Oklahoma State Bureau of Identification on Friday released a sketch of a tortoise-shell key ring that belonged to University of Oklahoma student Tracey Neilson, killed in her Moore apartment on Jan. 5, 1981. The key ring was 1-inch wide and 4-inches long with “Tracey” spelled in capital block letters. Cops believe the killer took it as a memento.

”In our experience, killers sometimes will take items from their victims,” OSBI Director Stan Florence said at a press conference, News 9 in Oklahoma City reported. “So we believe that the killer very likely took this key ring and also may very well still have it.”

Her husband, who found the body, made an emotional appeal for information at the press conference.

“With Tracey’s death, there is a huge emotional burden that placed on the family, extended family and everyone her life touched,” Dr. Jeffrey Neilson said.

“We ask anyone that has any information that would be helpful to come forward. We plead and we beg for that,” he said.

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Also released to the public during Friday’s press conference were crime scene photographs.

There’s a $100,000 posted by the Neilson family for information that leads to an arrest and conviction.

FoxNews.com reported in January that investigators had released photos of a cable repair ticket book found inside the Neilson apartment on the date of the murder.

The last ticket in the repair book is for work at Neilson’s apartment.  

Florence said the investigators have since learned the book was used by a Southwestern Bell worker but they have found no record of the employee who used the ticket book on the day of the murder.

OSBI investigators said anyone with information should call them at 1-800-522-8017.