SONNY Bono, former husband and singing partner of superstar Cher, was clubbed to death by hitmen on the orders of drug and weapons dealers who feared he was going to expose them, a former FBI agent claims.

Ted Gunderson, now a private investigator, has told the US Globe tabloid that Bono, who served as mayor of Palm Springs for four years, did not die after hitting a tree on a Nevada ski slope in January 1998 as everyone believed.

"It's nonsense for anyone to now try to suggest that Bono died after crashing into a tree. There's zero evidence in this autopsy report... to show such an accident happened. Instead, there's powerful proof he was assassinated.

"This was an evil plot that was carried out to almost perfection by ruthless assassins," Mr Gunderson told the paper.

The former agent, who has been researching Bono's accident for the past decade, said top officials linked to an international drug and weapons ring feared the singer-turned-politician was about to expose their crimes - so they had him killed on the slopes.

Bono, an experienced skiier, was ambushed on the slopes by hired hitmen, who beat him to death and then staged a tree collision, Mr Gunderson said.

He called for authorities to dig up Bono's remains and open a homicide investigation.

His claims have reportedly been backed by top forensics experts who fear Nevada authorities were too quick to call the death a skiing accident.

Investigator Bob Fletcher had also confessed he sent evidence of a 10-year study that linked top US government officials to arms and weapons dealers to Bono less than a month before his death, the Globe reported.

"(Bono) was going to make it his No.1 priority... There's no doubt in my mind Sonny was murdered by someone who needed him silenced," Mr Fletcher told the paper.

Originally published as Drug hitmen 'clubbed' Sonny to death