Kirby Archer is expected to plead guilty in exchange for prosecutors dropping the death penalty.
MIAMI, Florida (CNN) -- One of two men charged with killing the crew of the Joe Cool charter fishing boat last year has agreed to plead guilty to first-degree murder, a victim's relative said.
Kirby Archer is expected to change his plea to guilty in exchange for a prosecutors' agreement not to seek the death penalty against him, according to Jeff Branam, an uncle of slain boat captain Jake Branam.
He said prosecutors told the victims' relatives about the plea deal.
The U.S. Attorney's Office in Miami, Florida, declined to comment.
Court documents filed Friday show that Archer is scheduled to change his plea at a hearing Thursday.
Archer and Guillermo Zarabozo are charged with four counts each of first-degree murder, kidnapping and robbery in the deaths of Branam; his wife, Kelly; his half-brother Scott Gamble; and first mate Samuel Kairy.
None of the victims' bodies has been found, and authorities have said it is unlikely they will be.
The abandoned Joe Cool was found by the U.S. Coast Guard on September 23, floating about 60 miles south of the island of Bimini. Zarabozo and Archer were found a few hours later, about 10 miles away on a life raft.
The two had paid the Joe Cool crew $4,000 in cash to take them to the Bahamas from Miami, where they said they were planning to meet some girlfriends. The trip should have taken about an hour each way. The boat did not return.
Zarabozo told authorities the boat had been hijacked by pirates who fatally shot Jake and Kelly Branam and ordered the crew thrown overboard but spared the two of them.
This spring, Zarabozo said in court documents that Archer killed the crew, using Zarabozo's gun. No gun was found. Police believe that the bodies of the crew were pitched overboard between Miami and Cuba.
Jeff Branam said the victims' relatives met with prosecutors a few days ago. "They said he was going to plead guilty," he said of Archer.
"I would have liked to have seen him get the death penalty, but if he's going to be in prison for the rest of his life with no chance of getting out, that'll work."
CNN was unable to reach Archer's defense attorney.
Jeff Branam said the government's case against the two appears strong but said he's glad a jury won't decide Archer's fate.
"I think they have a lot of circumstantial evidence," he said. "If you have just one person on a jury who might feel there were pirates, they might not [convict]," he said.
"Without bodies, it could be an uphill battle."
Archer, 36, was once an Army MP who served at the U.S. Naval Base at Guantanamo Bay, Cuba. Investigators and victims' family members say they were told he wanted to go back to Cuba. Archer befriended Zarabozo, 20, who left Cuba with his family.
Last year, Archer fled to Florida after he was accused of stealing $92,000 from an Arkansas Wal-Mart where he was working.
Zarabozo's lawyer, William Matthewman, had little to say about Archer's pending plea. "All I can say is, Mr. Zarabozo pled not guilty. He maintains his not guilty plea, and he plans to proceed to trial."
No trial date has been set.
Jake and Kelly Branam are survived by their children: a girl who was 2 at the time of their deaths and a boy who was 4 months old. A court has awarded custody of the children to Kelly Branam's stepsister, according to relatives.