A previously convicted Thousand Oaks sex offender was sentenced to prison for crimes against minors and human trafficking on Tuesday.

Robert Ryan McGraa, 41, was sentenced to 15 years and four months in prison after pleading guilty to six felony charges related to human trafficking, possession of child sexual abuse material and luring a minor for a lewd purpose, according to the Ventura County District Attorney’s Office.

In 2019, investigators received a tip that McGraa had child sexual abuse material in his email account. Authorities discovered McGraa possessed “numerous images of prepubescent child females being sexually assaulted by adult males,” according to court documents.

He also “actively exchanged these types of images over the internet with other child sexual assault predators,” authorities said.

McGraa has a history of convicted sexual crimes against minors, the DA’s office said.

In 2005, he was sentenced to 16 months in prison for unlawful sexual intercourse with a minor among other sex crimes. Upon his conviction, McGraa was ordered to register as a sex offender.

In 2016, detectives received a tip that McGraa was posting nude images of a 15-year-old runaway. He had arranged for several suspects to pay for sex with the child victim. He later pleaded guilty to commercial sex trafficking of a minor and was sentenced to five years in prison.

McGraa is believed to have spent time in Thousand Oaks, Oxnard and Simi Valley and was very active on social media and the internet, officials said.

“Robert McGraa preyed on vulnerable individuals and exploited them for his own benefit,” said Rikole Kelly, a Deputy District Attorney who prosecuted the case. “Thanks to the courage of the victims, and the tenacity of Supervising District Attorney Investigator Terry Dobrosky and our other law enforcement partners, our community is now safe from McGraa’s dangerous and manipulative conduct.”

Authorities are urging community members to be aware of human trafficking signs and to call 911 to report suspicious activity. The public can contact the Forever Found R.E.A.C.H. Emergency Hotline for youth at 805-261-1212 or the Interface Human Trafficking Hotline for adults at 800-636-6738.