The former leader of a white supremacist gang who was sentenced to 66 years in Nevada prison for multiple crimes, including attempting to murder a fellow inmate, died a week ago after being incarcerated for more than two decades, officials said.

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James Wallis, 58, died July 31 at Centennial Hills Hospital in Las Vegas, Nevada Department of Correction announced Tuesday. His cause of death has yet to be released pending the results of an autopsy report.

Wallis started serving his sentence in 1995 after he was convicted in Clark County of attempted murder and other charges. He later became the leading member of the Aryan Warriors, a white-supremacist gang based in the Nevada prison system.

He was one of five reputed members of the Aryan Warriors convicted in 2009 of conspiring to engage in racketeering inside and outside of prison and participating in the earlier stabbing of a fellow gang member at the North Las Vegas jail.

Confirmation of his death was delayed until his family could be located. Members of the Aryan Warriors dawn distinct tattoos with Viking-related imagery, such as horned helmets, axes or shields, according to the Anti-Defamation League. Some of the shields include runic letters of an A or a W.

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The Associated Press contributed to this report.