Christopher Farmer and Peta Frampton left the coast of Belize on June 26, 1978, aboard a boat named the Justin B.

The young British couple in their mid-20s had decided to spend a year traveling abroad. They traveled to Australia and then went to the Americas. They toured Guadalajara, Mexico, and later wound up in Belize City, where they met an American named Duane, the owner of the Justin B.

They planned to take the bus to Merida in the Mexican state of Yucatán, but Duane offered to take them to Chetumal by boat. Farmer wanted to experience sailing, so they took Duane up on his offer, Frampton wrote in one of her letters to her mother. She wrote to her mother frequently, updating her on their travels.

On June 29, three days after they left Belize City, Frampton wrote her last letter.

Duane has two young sons with him, and he curses a lot and gets violent with the boys when things don’t go his way, she wrote. At the end of her letter, she said, “I don’t think there’s any more news — nothing much happens on a boat.”

She and Farmer were never heard from again.

About a week and a half later, firefighters found their bodies floating in the Caribbean Sea, off the coast of Punta De Manabique in Guatemala, their bodies hogtied.

Autopsies revealed that the two had drowned.

The deaths of Farmer, a recent medical school graduate, and Frampton, a new law school graduate, would remain a mystery for the next four decades.

Finally, earlier this month, federal authorities said they think Farmer and Frampton were murdered by Silas Duane Boston, the boat owner.

Boston, now 75, has been charged with two counts of maritime murder. He was arrested in Paradise, a small unincorporated town in Northern California, the Sacramento Bee reported.

The charges came after a break in a separate cold case investigation of the disappearance of Boston’s wife, Mary Lou, who vanished in Sacramento in 1968 — 10 years before the British tourists are believed to have been killed.

According to a federal criminal complaint, two witnesses — Boston’s two sons aboard the Justin B — had provided a detective investigating Mary Lou’s disappearance with a detailed account of how Farmer and Frampton were killed.

Boston’s sons told police that at that time, when they were 12 and 13, they were living with their father in Sacramento. They left after a violent incident involving their father and another woman, court records say. Boston took his sons to get passports and snorkeling and scuba-diving gear, and the three drove through Mexico to Belize. There, Boston, then 37, bought the Justin B, named after his other son, and started taking tourists on boat tours.

Then, they met the young couple from Chestire, England. While on the boat, the two were always writing letters to their families about their trip, one of his sons told police. They also took photos using Farmer’s film camera. One photograph — which was later turned over to police — depicts Farmer with Boston’s two sons.

One night, when the boat was anchored in the harbor near the port of Livingston, Guatemala, Boston, completely unprovoked, attacked Farmer several times, his sons told police. First, he hit Farmer with a billy club as the latter was pulling up the boat’s anchor. He also tried to stab him in the chest with a fillet knife, but it broke. Then, Boston tackled him, tied him up at the front of the boat, and then tied up Frampton in the galley, court records say.

The next morning, Boston moved the couple to the edge of the boat. Court records say he hogtied them, tied machine parts to the ropes, covered their heads with plastic bags and pushed them into deep water.

Boston looked at his watch, one of his sons said. After three or four minutes, he said, “Okay, they are dead now.”

Then, the Justin B sailed away.

For a couple of hours, no one said anything.

Then, Boston said, “You know, I had to do that. They didn’t give me a choice.”

On July 6, 1978, Boston and his sons reached the Livingston port in Guatemala. There, Boston dropped off Farmer and Frampton’s clothes at a local business, one of his sons told detectives. He also mailed Frampton’s last letter to her mother, so that her family would think the couple was still alive in Guatemala.

The letter was postmarked July 18, 1978 — 10 days after the couple’s bodies were found off the coast of Punta De Manabique, about 10 miles northeast of Livingston.

Boston later told authorities who were investigating the tourists’ disappearance that he dropped them off at a peninsula across the bay from Livingston because his boat needed repairs. He said he may have seen them getting on a ferry in Livingston, but he wasn’t sure.

Why Boston allegedly killed the tourists isn’t completely clear.

Boston’s sons told detectives that shortly before the incident, Boston got drunk and started punching younger son. Farmer tried to help the boy, prompting Boston to attack him instead, court records say. But Boston fell into the water after he tried to hit Farmer and missed. That’s when Boston began plotting to kill the tourists, his sons told police.

Over the years, Boston told at least one other person about the alleged murders, court records say.

That person, Boston’s old traveling companion, told detectives that he and Boston spent a year in Mexico in the early 1990s. Boston told him about the tourists’ deaths one day while they were driving together. He was laughing as he nonchalantly told his friend that he killed the tourists for fun, court records say.

To this day, Boston’s sons, who are now in their 50s and are estranged from each other, fear their father, they told detectives. They described him as a vindictive man who carefully plans his retaliation.

Shortly after the tourists’ deaths, Boston, again in a drunken stupor, threatened to kill his sons, court records say. He told them that he had also killed their mother, Mary Lou, by gunning her down as she was running away from him.

Boston had told investigators that she had taken money from their joint bank account and run off with another man.

Over the years, Boston, who is fluent in Spanish, fled to Mexico every time he became aware of a criminal investigation involving him. He stopped traveling because of his failing health.

Boston is not charged with any other deaths.

He appeared in federal court in California on Dec. 8. His attorney, Douglas Beevers, said in court that Boston, now in a wheelchair, suffers from arthritis and has difficulty hearing, according to the Sacramento Bee.

The crimes Boston is charged with are punishable by death, but prosecutors will not seek that punishment, according to court records. He could face life imprisonment.