Prominent Israeli crime boss Charlie Abutbul was found dead on Thursday at his home near Tel Aviv, apparently from a self-inflicted gunshot wound, public radio said.
Abutbul, who had survived several attempts on his life, had been due to serve a 16-month jail term after being convicted of abduction.
He was under house arrest pending his imprisonment.
Public radio said it appears the man, aged in his 60s, committed suicide at his Netanya home, but added that police were still investigating his death.
Organised crime gangs in Israel have been engaged in an often violent struggle over the past few years, prompting police to set up a special task force, Unit 443, to tackle the issue.
Around a dozen Israelis are believed to have been killed in violence between crime families, including Abutbul's uncle Felix, who once headed the clan, and a nephew.
Two of Abutbul's sons are also serving jail sentences.
In February, Prime Minister Benjamin Netanyahu declared war on organised crime, saying that police should use both existing and "new means" against gangsters.