Sonoma County jurors on Wednesday convicted a 51-year-old Santa Rosa man of having unlawful sex with three teenage girls, furnishing them with drugs and videotaping the illicit encounters at his Bennett Valley apartment.

However, the panel failed to find John David Heglin guilty of three of the most serious of the 20 charges — forcible rape, rape by intoxication and pandering.

Jurors leaving the courthouse said they had questions about testimony from key witnesses, including the three victims.

"There just wasn't enough evidence to convict him," said one woman juror who refused to give her name.

Prosecutors said Heglin met two of the girls in 2009 at a birthday party in his apartment complex. He plied the then-16-year-olds with alcohol and drugs and later offered them money for sex, prosecutors said.

Heglin allegedly boasted to the girls that he had contacts in the adult film industry and promised to get them work on a party boat for "sex tourists" — men who would pay them to dance and have sex with them.

At some point, the teens introduced Heglin to the third girl, who was their friend. He was arrested last February after the girl told her mother Heglin gave her drugs and raped her.

Heglin did not testify. His lawyer, Geoffrey Dunham, said the sex was consensual.

Jurors began deliberations Feb. 16 after about two weeks of testimony. They revisited key pieces of testimony and watched one of the many sex tapes. Detectives said the tapes showed Heglin and the teens having intercourse, oral sex and using vibrators.

Heglin faced life in prison if convicted of raping a drugged victim, prosecutors said.

Instead, jurors returned guilty verdicts on 15 felonies, including eight counts of oral copulation with a minor, two counts of providing drugs to an underage person, three counts of unlawful sex with a minor, a count of sexual penetration and possession of child pornography.

Now, Heglin is exposed to about 20 years behind bars and lifetime sex offender registration. The next hearing is April 11.

District Attorney Jill Ravitch said inconsistent witness statements hampered the prosecution.

"These are difficult cases," Ravitch said. "We respect the jury's verdict."