Michael David Cornett, 46, was convicted of seven felony sexual assault counts and several enhancements, including being an habitual sex offender.
Sonoma County District Attorney Stephan Passalacqua said the victims were six and 10 years old when the offenses occurred.
Cornett was unaware the girls' 13-year-old brother photographed him molesting one of the girls. The brother reported the crime and testified at Cornett's two-week trial before Sonoma County Superior Court Judge Rene Chouteau, Passalacqua said.
Chouteau sentenced Cornett to three consecutive life terms, Passalacqua said.
Cornett was convicted in 1996 in Marin County for molesting his then 9-year-old stepdaughter from a previous marriage, Passalacqua said. That victim, now 23, testified at the Sonoma County trial about the abuse Cornett inflicted on her years ago, Passalacqua said.
