It’s not a mystery how the Coulthurst family and a group of teenage deckhands were killed on their fishing boat, Investor, on Sept. 6, 1982, in the tiny southeast Alaskan fishing village of Craig.
What remains unknown, more than 35 years later, is who did it — and why.
“You never stop thinking about them,” says Dave Freeman, who grew up with Jerome Keown and Dave Moon, two of the massacre’s eight victims.
“The shock of losing everyone really tore up our town,” Freeman tells PEOPLE. “They all had their whole lives in front of them, and they were just blown away. It’s just such a shame and tragic for no reason.”
The slaying of skipper Mark Coulthurst and his pregnant wife, Irene, both 28, along with their children Kimberly, 5, and John, 4, and four deckhands — Chris Heyman, 18; and Keown, Moon and Mike Stewart, all 19 — is still Alaska’s worst unsolved mass homicide.
The case will be featured on Monday night’s People Magazine Investigates, on Investigation Discovery, and in this week’s issue, on newsstands now. The PMI episode is exclusively previewed above.
Here are five things to know about the case.
• For more on this case, subscribe to PEOPLE or pick up this week’s issue, on newsstands now, and watch People Magazine Investigates: Murder at Sea on Monday, Dec. 11, at 10 p.m. ET on Investigation Discovery.
1. The Killer Moved in Plain Sight
Hours after shooting his victims with what police believe was a .22-caliber pistol or rifle, the gunman fired up the engines on the 58-foot, $850,000 Investor, waving nonchalantly to a nearby skipper as he moved the vessel — with his victims’ bodies inside — to a secluded bay a mile outside of town.
He motored back to the weather-beaten docks in the Investor’s skiff, returning the next afternoon with a can of gasoline to set the craft ablaze before speeding back to town and then vanishing.
Authorities would later describe the suspect as a white male in his early 20s with a pockmarked complexion.
“When I got there [to the boat], black smoke was coming out of the wheelhouse, but there was nobody on deck,” former Craig police chief Ray Shapley recalls in a story about the Investor killings in this week’s issue of PEOPLE. “It made the hair on the back of my neck stand up.”
2. Slain Family Celebrated Soon Before Death
Police said Mark, who was based in Blaine, Washington, and his crew arrived in the rowdy town of Craig, Alaska, on Sept. 5, 1982, shortly before for the final days of the commercial fishing season.
The ambitious, hard-working and well-liked skipper had recently become the proud owner of one of the most expensive, high-tech commercial fishing boats of its kind in the region.
“Every one of his crew wanted to be like Mark,” recalls Keown’s older brother Brian. “He was one of the best skippers around.”
Hours before the family was killed, Mark and his wife and kids attended a birthday party thrown for him at a restaurant near the docks, returning around 9:30 p.m. as a storm began to rage.
The killer then crept onto the Investor in the darkness, police said, and executed his victims.
3. Prime Suspect Has Been Exonerated
Two years passed before police arrested John Peel — who once worked for Mark and who had been working on another fishing boat and claimed to be asleep at the time of the killings — based on his similarity to sketches of the suspect.
Peel’s first trial in 1986 hinged on circumstantial evidence and lasted over six months. Prosecutors suggested that he committed the murders because of a falling out he’d had with Mark. It ended in a hung jury.
After being found not-guilty in a retrial two years later, Peel filed a wrongful prosecution suit against the state to recoup his legal fees and was awarded a reported financial settlement of $900,000.
Police are no longer looking for the killer. “The case is closed,” says Tim DeSpain, spokesman for the Alaska State Troopers. But the Investor slayings are hardly resolved.
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“It was a pretty damn good investigation,” says former Bellingham, Washington, police detective David McNeill, who helped Alaskan authorities investigate.
“They got the right guy,” McNeill says. “Just because someone is acquitted doesn’t mean they’re innocent, just means there’s not enough evidence to show guilt beyond a reasonable doubt.”
“Somebody out there knows what happened,” Peel tells PEOPLE in this week’s issue, in an exclusive interview after years of silence.
“Somebody was responsible for this,” he says. “Somebody out there knows what happened, but I’m not going to waste any more of my life on it.”
4. Motive Was Never Clear
Craig’s former police chief Shapley is convinced the killings were the result of a drug deal gone bad.
“I’ve heard a lot of talk that it was a drug boat,” explains Shapley, who spent days sifting through the ashes on Investor for bone fragments and teeth. “They say Craig floated on drugs in those days.”
But McNeill describes the drug angle as “a bunch of bull crap.”
“They charged the man they felt was responsible, and he was acquitted,” he says.
5. Victims’ Friends, Family Still Live in Shadow of the Crime
Those whose who knew Mark say he was born to fish. “He was just an incredibly hard worker who always said he was going retire by the time he was 50, and I never doubted it,” recalls his younger sister Laurie Hart.
He “always had irons in the fire,” she says. “He was making money.”
For decades Hart was convinced of Peel’s guilt, but her opinion changed last year after he agreed to meet with her and her sister at a local diner and answer their questions.
“I don’t know if he’s actually the one who pulled the trigger,” Hart says. “But I think he knows more than he’s saying.”
For those whose lives were upended by the killings — including Peel — the case remains a painful cloud that refuses to lift.
Says Freeman, who knew both Keown and Moon: “It’s hard to move on because there are just no answers.”
People Magazine Investigates: Murder at Sea airs Monday (10 p.m. ET) on Investigation Discovery.