WHEELING -- In the morning hours of June 13, 1977, Postulate Nun Roberta "Robin" Elam walked to a peak on the grounds of Sisters of St. Joseph in Wheeling to have some alone time. She was attending a retreat at the convent.

Sometime while observing a moment of silence, she was attacked by a man, raped and strangled. Her killer was never found.

Thirty years later, the investigation into her death continues with the help of a DNA profile taken from evidence collected that day.

Cold case detective Sgt. Dan Swiger with the State Police and the Ohio County Sheriff's Department have spent countless hours working to put that man behind bars.

Swiger said he's worked this case for five years and talked to many persons of interest.

"Up to this point, everybody we've talked to has been cooperative. Some of them are inquisitive. Why are we working on this 30 years later. And my answer is why not? Why should we not be working on this," he said.

He and Detective Joe Cutcha with the sheriff's department continues to fight, but he admits it's been a roller coaster ride.

"It starts building up only to be let down and that's happened many times. At this point, we've cleared in excess of 30 people in this investigation, and there's still more people that a person of interest. The potential suspect pool or person of interest in quite large," Swiger said.

He believes Sister Robin's killer is still alive, and will be caught.

"I'm working on a case right now from 1950 that the suspect could be still alive. They may be in their 80s or 90s, but do you give up just because someone is old? No. It's still open. A big part of cold case investigations is about bringing closure to the families. It's not about making an arrest," Swiger said.

Ohio County Sheriff Tom Burgoyne was a young FBI agent in Wheeling when the murder occurred, but he still ranks it at the top of his list.

"We've had several vicious murders in this community since I've been here in the 1960s, but that fact that this woman was a woman of the cloth sets it apart from every other case I've ever investigated from a murder standpoint, " said Burgoyne.

That's why he wants to see it solved.

"It's probably one of those things that keeps me awake at night. And sometimes it's the first thing I think about in the morning. And you'd think after 30 plus years, you wouldn't be thinking about this," he said.

The case is now getting national attention. The story will air in a Discovery Times special called, "Sensing Murder: Convent Murder."

It will air Thursday, June 14 at 8 p.m. on the Discovery Times Channel, Comcast Channel 111.