But despite his incriminating profile, Henry had an alibi. 'I can prove where I was at on the dates that you said this happened,' Henry told investigators. He said he was at a hospital in Monroe, N.C., where his wife was staying. 'I suppose you will take my word.'
'Mr. Henry,' replied one of the officers, according to the files. 'Right now I don't believe I would take your word for anything.'
In an effort to corroborate his alibi, cops timed the drive from the hospital to the crime scene and concluded there was no way Henry could have raced back in time to see his wife. Even with knowledge of his mental health and lying twice about the gun, they set him free.
Now dead, Henry will never have the chance to erase the suspicion or to confess.
Passing through
Evidence says the young couple weren't from South Carolina.
'If they were from around here we would have found them by now,' says Sumter County Coroner Verna Moore. In 1976, she was deputy coroner and also worked for the local paper, The Sumter Daily Item.
Moore persuaded 'Unsolved Mysteries' and Court TV to run specials on the case, but still no one came forward. For the past year she's been working with a cold case investigator in Virginia to sift through evidence for new leads.
She hasn't given up yet. 'Somewhere out there they've got family still looking for them,' she says, 'and hitting all the wrong places.'
But with their olive skin and ethnically ambiguous faces, the couple could have come from anywhere. 'We've made contact with agencies in Argentina, Uruguay, Brazil, even in the Mediterranean,' Moore says.
Sgt. Ray Mackassey, a forensics officer in charge of the evidence in the case, says that while the case came many years before his time, he has heard the couple may have been Canadian.
Meet Jacque
Months after the homicide, an employee of KOA campgrounds near Santee, S.C., called authorities, believing he had earlier made friends with the dead man, who went by the name 'Jock,' according to documents in the case file.
Jock, or more likely, Jacque, stayed a few days at the campgrounds with his young female companion, then left for Florida. He and his girlfriend stopped at the campgrounds again on their way back.
The two men became friends. While shooting pool, Jacque told the KOA worker he was the son of a prominent doctor in Canada who had disowned him for giving up on his own career in medicine. He was taking a vacation of sorts, traveling the country aimlessly.
Before leaving, he tried to pawn an expensive ring to the employee, who later told authorities that the ring had looked a lot like the one found on the mystery man.
Inside his pocket was a book of Grants Truck Stop matches, which could only be found in Idaho, New Mexico and Nebraska. Authorities think Jacque passed through these places on his travels.
Parnell and his deputies seem to have made some effort to follow the Canadian trail. They wrote to the Royal Canadian Mounted Police, which in turn published fingerprints and sketches in its trade magazine. Nothing ever turned up.
Priceless items
The dead man's ring, made of 14k gold, had the letters 'JPF' engraved on the inside.
Wolfgang Stihl, the Virginia cold case investigator who's been working with the county coroner, speculates family members gave him the ring, along with the Bulova Accutron watch he was also wearing.
Stihl has determined by markings on the watch that Bulova made the piece in 1968. But the company trashed its records when downsizing shortly thereafter, so no one knows where the watches were distributed.
But Stihl is sure about one thing. 'That watch was bought the year it was made.'
It could have been a high school graduation present, based on the victim's estimated age, 26 or 27. 'It was a popular item back in those days,' Stihl said.
The dead man was also wearing a Coors Light of America T-shirt, the same one sold at a car race held in Florida. More evidence to support the KOA lead.
The girl was also wearing expensive rings that look Mexican in style.
Stihl says the rings were probably handmade, and he hopes to use symbols on the inside of the bands to identify the artist and perhaps identify places where the girl bought the jewelry.
Latest leads
There are a few more unexplored avenues.
One involves a plaster cast or photographs of the tire tracks found at the murder scene, which Stihl says he can use to identify the getaway car.
'Every car has a different wheel-base area,' he says. That and tire tread marks could help him determine the year and make of the vehicle.
Stihl says there are many things about the case that bother him. He doesn't understand why the killer would have stolen cars, wallets or purses, but left watches and jewelry. The girl wasn't raped ' her autopsy didn't turn up a trace of sexual assault.
According to an examination of entry wounds, the murderer shot both victims in the back of the head to finish them off. 'These were executions,' he says, adding the killer may have been a traveling companion. That would explain why the jewelry wasn't stolen. The killer cared only about erasing their identities.
There's one last thing Stihl finds startling. 'They were completely clean. No dirt under their fingernails, none in their hair.'
They weren't smokers and they weren't drinkers. The man in particular was tall and athletic looking, possibly an aficionado of contact sports, judging by the suggestive scars on the back of his shoulder. Overall, the couple likely came from the upper crust of society.
Forever unsolved?
Stihl says he's confident he can identify the couple, though their killer may never be revealed. 'I wish I'd been there,' he says, adding that it would have been easier to work the case before most of the evidence dried up.
The ugly truth is most local law enforcement agencies have never possessed the resources or manpower to crack bizarre cases, though the small town of Sumter has seen its fair share of those, being home to serial killer Donald 'Pee Wee' Gaskins Jr. There are more than 20 unsolved cases in Sumter County.
These two killings are among the oldest.
Sumter Sheriff Tommy Mims wants to see this particular case solved as much as anyone, but he knows the odds of identifying the victims are evaporating.
'This case has been hashed up one way and down the other,' he says.
The mystery couple's parents, aunts and uncles may lie in their own graves by now.
But others refuse to let go. 'I've worked on this for almost 20 years,' Moore says. She's vowed not to give up until her career is over. But if she's re-elected this year, it will be her last term as coroner.
That's unimportant, she says.
'Whoever takes my place will keep working on it.'