MIAMI, Florida (CNN) -- Family of the missing crew members of the Joe Cool fishing boat found a fourth bullet casing on the boat and turned it over to the FBI, a relative said.
A file photo of the Joe Cool, a charter fishing boat found derelict in the Florida Straits.
The FBI is investigating whether two men who hired the boat -- Kirby Archer and Guillermo Zarabozo -- killed the four-member crew.
Jeffrey Branam, the uncle of the boat's captain, told CNN the casing was found on the Joe Cool fishing boat by his son and a crew member while the FBI was returning the boat to them Thursday.
"We had to prep the boat and fill it with fuel to get to the engine, " Branam told CNN. "To get to the hatch, we had to move the furniture and when we moved the couch, we found the casing."
FBI spokeswoman Judy Orihuela said the agents who were there removed the 9 mm casing -- the same size as three others that were found.
Orihuela said when the boat was first searched, it did not appear the couch was movable.
At a bond hearing Monday for two men who are under investigation in the case, authorities said they recovered three other casings. They said two of the casings were found inside the boat's cabin.
"Now you have four casings and four people [presumed] dead," Branam said.
Branam said it did not appear to him that anyone tried to sink the abandoned boat. Federal agents have said it was a mess when they found it.
About 10 miles away from where the boat was found, the Coast Guard found Archer and Zarabozo aboard one of the Joe Cool's life rafts.
The two men, who had paid $4,000 cash almost two weeks ago to charter the boat for a one-way trip to the Bahamas, are being held without bond.
Archer is charged with unlawful flight on an Arkansas warrant, accused of stealing more than $90,000 in cash from a Wal-Mart where he once worked.
His traveling companion, Zarabozo, a 19-year-old licensed security guard, is charged with lying to a federal agent.
Archer and Zarabozo said the Joe Cool was attacked by three Cuban hijackers who shot the four crew members. Zarabozo said he was ordered to throw the bodies overboard.
On Tuesday, a judge said he believes circumstantial evidence shows four homicides took place.
A Coast Guard agent said two bullet casings and suspected blood were discovered inside the cabin, despite Zarabozo's assertion that the four crew members were shot outside the cabin. A third bullet casing was found outside the cabin, he said.
"Your theory is [Archer and Zarabozo] killed the four?" the judge asked the assistant U.S. attorney at the bond hearing. "Yes, your honor," the prosecutor replied.
Arraignment is set for next week. The men are not charged with murder.
The Coast Guard spent five days searching for Capt. Jake Branam, his wife Kelly, Jake's half brother Scott Gamble and first mate Samuel Kairy.
Saturday morning, relatives of the crew will stage a memorial at sea near the Port of Miami. Four air horns will sound in memory of the four crew members.
"It's difficult," Branam said. "Some relatives still think the four are alive and are still searching for them."
He said they've removed the name of the boat from the stern and will retire the name from their charter fishing business. They will likely retire the boat, too.
Referring to Archer and Zarabozo, Branam said: "I'd like to use them as shark bait." E-mail to a friend