Provincial police hope a case chronology video can help breathe life into a four-decade-old homicide.

At a news conference Thursday, OPP unveiled a YouTube video detailing the circumstances surrounding the death of 14-year-old Sarnia high school student Karen Caughlin.

Det.-Insp. Dave Truax says "No investigation is closed until it is properly resolved...This video provides an additional method of stimulating a request for information on this investigation."

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

Investigators say she never entered the home and a farmer discovered her battered body later that morning in a shallow ditch by then 6th Side Road or Freer Road, now known as Plowing Match Road northwest of Petrolia.

The OPP Criminal Investigations Branch says they are looking at a nine-hour gap between when Caughlin was last seen and when her body was discovered 22 kilometres away.

Police are hoping the seven-minute video will jog the memories of Sarnia residents. Authorities want to speak with anyone who may have seen or been with Caughlin on Friday, March 15 at locations in the community or at Sarnia Collegiate Institute and Technical School.

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 along Oil Heritage Road north of Petrolia, led investigators to rule her death a homicide.

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

Still, anyone with information is asked to contact Lambton County OPP or Crime Stoppers.

Det. Chris Avery says "Whether they think it is important or not, especially if we have not yet spoken with you, I would like the opportunity to gather their information."

As for Caughlin's family, they have not given up hope that the person responsible for her death will be found.

Marylou Schwemler says she's still shaken by the murder of her younger sister, "As the time goes on you wouldn't think it would be as hard, but it goes right back 40 years for us...We'll never give up on Karen. That'll never happen. It is just how we personally are going to put this somehwere in our hearts."

Sunday marks exactly 40 years since Caughlin was found murdered and the family is publishing a memorial in the local paper to mark the sad anniversary.

It reads in part "Forty years with endless tears. An unforgivable crime that has not healed with time."

With files from The Canadian Press