The Trail Went Cold – Episode 315 – Hugh & Dian Harlin, Larry Costine & Melissa Jo Sermons

October 13, 1982. Morro Bay, California. The decomposed body of 43-year old Dian Harlin is discovered in a stand of trees next to a beach and she has been strangled to death with a leash belonging to one of her dogs. It turns out that Dian’s eccentric 47-year old husband, Hugh Harlin, had failed to report her missing for eleven days and since the couple was known for having a turbulent relationship, Hugh becomes a potential suspect in his wife’s murder. Four years later, Hugh inexplicably vanishes without a trace after his abandoned pick-up truck is discovered by the side of the highway. Investigators are unable to determine if Hugh’s disappearance is connected to Dian’s murder, but both cases are never solved.

May 3, 1992. Polk County, Florida. After attending a rodeo, 31-year old Larry Costine and his 26-year old girlfriend, Melissa Jo Sermons, return to Larry’s mobile home. Larry’s nude body is eventually discovered inside the trailer and since he was shot four times and Jo has gone missing, investigators initially suspect that Jo killed Larry and went on the run. However, two decades later, law enforcement announces that they now believe Jo was a victim and was murdered by the same person who shot Larry. While Jo’s ex-boyfriend is considered to be the prime suspect, there is not enough evidence to charge him with the crime and Jo is never found.

On this week’s episode of “The Trail Went Cold”, we cover two unsolved mysteries in which one half of a couple was murdered while the other half went missing.

If you have information on the Hugh & Dian Harlin case, please contact the Morro Bay Police Department at (805) 772-6225. If you have information on the Larry Costine & Melissa Jo Sermons case, please contact the Polk County Sheriff’s Office at (863) 533-0344.

Additional Reading:

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“The Trail Went Cold” is doing a weekly livestream show on Vokl every Thursday from 7:00-8:00 PM ET as part of their “True  Crime Thursday” line-up. For more information, please visit their website.

“The Trail Went Cold” is going to be appearing on podcast row at “Crimecon UK” at the Tower Bridge, Leonardo Royal Hotel & Spa in London on June 10-11, 2023, as well as “Crimecon” at the World Center Marriott in Orlando, Florida on September 22-24, 2023. To get a 10 % discount on the purchase of tickets to either event, please use our specialized promo  code, “COLD23”, by visiting or

The Trail Went Cold is produced and edited by Magill Foote.

All music is composed by Vince Nitro.