Prosecutors in Tahiti made the decision to open a murder investigation into the disappearance of former NBA player Bison Dele based on comments from the former girlfriend of Dele's older brother, the Los Angeles Times has reported.

The police official told the newspaper that Erica Weise told the FBI that Dele's older brother, Miles Dabord, informed her in a telephone conversation of a struggle aboard Dele's boat, the Hakuna Matata, that resulted in the deaths of Dele, his girlfriend, Serena Karlan, and the boat's captain, Bertrand Saldo.

In another report, the three were believed to have been murdered with the basketball player's own handgun, the chief prosecutor for the territory of French Polynesia told the Agence France Presse news service Wednesday.

"There is also every reason to believe that they were murdered and that a handgun was used," Chief prosecutor Michel Marotte told the AFP on Wednesday.

Investigators spoke with several eyewitnesses, who said they were "almost certain" a gun was aboard, even though Dele didn't declare one when his boat arrived in Tahiti.

Dabord reportedly deflected blame from himself, claiming during the phone call that the fight was started by Dele, the Times reported.

The call was reported to the FBI and the Sonoma County, Calif., Sheriff's Office. Sonoma County deputies confirmed they had received a phone call and forwarded the information to the FBI.

On Tuesday, Tahitian officials upgraded the investigation from a preliminary inquiry to a premeditated murder investigation. A premeditated murder investigation is the most serious level of any homicide charge under French law, the chief prosecutor for the territory of French Polynesia, Michel Marotte, told the Rocky Mountain News.

Dele, Karlan and Saldo have been missing since they left Papeete, Tahiti's capital city, aboard Dele's boat July 4. The boat was later found -- repainted and renamed -- in a private slip on Tahiti. Witnesses have said Dabord was seen docking the empty boat on July 15. He left the island two days later.

Dabord is wanted on two arrest warrants issued in connection with his allegedly posing as his brother to buy more than $150,000 in gold coins in Phoenix. Dabord is still at large and was last spotted in Tijuana, Mexico.

Officials with the FBI have refused to comment on the case. But Marotte confirmed to the Rocky Mountain News that the FBI is investigating phone calls made about what happened on the boat.

Marotte said the U.S. Department of Justice on Tuesday officially requested the assistance of the French government in their investigation into the disappearance, adding that there are still two independent and parallel investigations being conducted, one by the U.S. and one by French law enforcement authorities.

Authorities spent Tuesday trying to construct a timeline of each person's activities on the boat, Marotte said.

Meanwhile, Police said Wednesday that investigators were scouring Dele's 55-foot catamaran, taking photographs and gathering fingerprints and other evidence for analysis.

Investigators have found "nothing spectacular'' on the boat, Investigating Judge Jean-Bernard Taliercio was quoted as saying in Tuesday's edition of the daily La Depeche de Tahiti.

"No bodies, but some very interesting things,'' he said without elaborating. "This operation should take several days.'' A team of 13 FBI agents was assisting authorities.

Newspapers quoted witnesses who spotted the boat before it was docked. A fisherman quoted by Nouvelles de Tahiti but not identified by name said he saw the catamaran hit rocks around Hitia'a, on the eastern Tahitian coast, on July 13 and stayed in the area for three days.

A gas station manager in Hitia'a said a large man "came to the station and wanted to repair his boat.'' The man, who asked not to be identified by name, directed him to the Taravao marina. The man then went to a second service station in the town.

Dele and his girlfriend apparently spent much of their time in the area on the island of Moorea, 10 miles away. The director of the Moorea hotel Sofitel La Ora, Didier Lamont, has said the couple checked in shortly after June 16.

Information from The Associated Press was used in this report.