Karen Caughlin Homicide Portrait

The body of Karen Caughlin was found by a farmer in a shallow ditch near a gravel sideroad northwest of Petrolia, Ont. (Courtesy Sarnia Police)

Ontario Provincial Police hope a new appeal to the public will help reinvigorate an investigation into a four-decade-old homicide.

Karen Caughlin, 14, of Sarnia, was dropped off early on March 16, 1974, in front of a friend's house on Brock Street  South in the city.

Police on Thursday released a seven-minute video detailing the events of the day Caughlin died.

Her older sister, Mary Lou Schwemler, hopes the video helps bring closure for the family. 

"We would like to have Karen rest in peace and we can't do that until somebody who knows something comes forward and puts an end to this," she said. "I don't personally think we'll ever have closure unless someone out there grows a heart."

Caughlin spent three hours roller skating at Rose Gardens Roller Rink before being dropped off out front of 238 Brock St. S. just before 1 a.m.

Investigators said Caughlin never entered the home, and a farmer discovered her battered body later that morning in a shallow ditch by a gravel sideroad northwest of Petrolia.

She was found on what was then known as 6th Sideroad, or Freer Road. It's now known as Plowing Match Road, between Churchill Line and Lasalle Line in Lambton County.

Police have said the autopsy revealed that Caughlin's injuries were consistent with having been struck by a vehicle. However, circumstances such as her purse being located several days later in a ditch north of Petrolia, led investigators to rule her death a homicide.

Caughlin's body was found at 9:50 a.m., 22 kilometres away from the house where she was supposed to spend the night. Her purse was found at the bottom of a ravine, another 1.6 km away from her body.

Even a $50,000 reward for information leading to the conviction of her killer hasn't led police to an arrest in the case.

"This investigation has been ongoing for 40 years," Det. Insp. Chris Avery of the OPP criminal investigation branch says in the video.

"We would like to bring it to a conclusion and provide closure to the Caughlin family. It’s my hope the video will stimulate memories of persons who were in the area of Brock Street South and Wellington Street in the early morning hours of March 16, 1974."

Police believe the person or persons responsible for Caughlin's death are still alive, which is why the case remains open but not yet solved.

"There are persons of interest and people under investigation," said Avery.

"It had to be someone she knew. She would not get into a car alone unless she knew that person," said Schwemler.

Another sister, Kathy, is unhappy with the way police have dealt with the case.

She claims they haven't followed up on some tips.

Two years ago, she organized a protest outside the OPP office in Petrolia, demanding an independent review.

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With files from CBC News