Mark Vanderhoof had a lengthy history of brutalizing young children. In 1980, he was convicted of child abuse for the physical assault of his 4-month-old daughter in Nevada.

Five years later in Oregon, he picked up a girlfriend’s 4-year-old daughter by the throat, threw her down and bashed her head against the wall in Douglas County. In 1988, he was convicted of raping his fiancee’s 4-year-old daughter in Douglas County, leaving strangle marks on her neck. He spent 12 years behind bars.

But when Briana Snow began seeing Vanderhoof and moved into his Roseburg area home in September 2010, she had no idea of his violent past or that Oregon had designated him as a predatory sex offender. He told her he’d spent time in prison for a sex-related offense, but claimed the sex was consensual with an underage woman, she said.

Four months later, Snow came home to find her 2-year-old son, Dennis James “Bubba’’ Young, unconscious and unclothed with a severe head injury. The toddler died three days later. Last April, a Douglas County judge convicted Vanderhoof, now 53, of murder by abuse in the boy’s death and sentenced him to life in prison, with the possibility of parole after 25 years.

Had Vanderhoof's face and personal information been posted on Oregon's sex offender website, the 2-year-old's killing could have been prevented, lawyers for the boy's estate argue in a wrongful death lawsuit filed against the state this week.

The tragic case, the lawyers say, highlights the inadequacy of the state's public website. The site lists only a small percentage of predatory sex offenders.

The suit also alleges that the state failed to take action after a Douglas County parole officer in 2006 advised Oregon State Police that Vanderhoof should be added to the website while Vanderhoof was still on parole and after the officer made it clear that doing so should be a "high priority.'' The state says it never got the proper notice.

“This would not have happened if he’d been on that website,’’ said Erin K. Olson of Portland, one of two attorneys representing the toddler’s estate. “If a sex offender has been designated as predatory, they should be on it.’’

The lawsuit seeks $1.6 million in damages from state police, who manage the sex offender website, and from the state Department of Corrections, which oversees the parole officer.

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The names, photos and criminal histories of only 2.5 percent of Oregon’s 25,354 sex offenders appear on the website for people to search. By state law, Oregon limits the public site to certain predatory sex offenders -- only those who meet three special criteria. Currently, only 30 percent of the state’s predatory sex offenders are on the website.

Olson and attorney Scott C. Lucas argue that photos of all the state’s predatory sex offenders should be made public. Federal law adopted in 2006 requires states to publicize considerably more information on sex offenders on the Internet, but Oregon hasn’t complied.

“The information should be readily available to the people it could protect,’’ Olson said.

State officials have said they had no authority under Oregon law to place Vanderhoof on the sex offender website and have denied the attorneys' claims. They declined further comment this week, citing pending litigation.

In Vanderhoof’s case, the mother of his 4-year-old rape victim had contacted the state police Sex Offender Registration Unit in 2006 and asked why Vanderhoof wasn’t on the website. A unit employee then sent an email to Vanderhoof’s parole officer on Oct. 18, 2006, asking if he thought Vanderhoof should be added to it.

Douglas County parole officer John Skourup, who was assigned to Vanderhoof, responded that he had already submitted a request to the state to add Vanderhoof, but it hadn’t happened for some reason, according to state records. Skourup advised the state police employee that he would work with someone within Douglas County Community Corrections to make it “a high priority for this to happen,’’ the state records show. There’s no dispute: Vanderhoof’s name never made it on the website.

“Somehow the ball was dropped,’’ Lucas said.

Under Oregon law, an offender’s supervising agency must notify the Sex Offender Registration Unit and provide the information to be posted. But the unit never received the parole officer’s notification or information on Vanderhoof during his parole supervision, and the state had no legal authority to post Vanderhoff on the website once he was off parole, according to the Oregon Attorney General’s Office.

Predatory sex offenders, under state law, only make the website if they meet three criteria: They must be designated as predatory sex offenders; authorities must have notified the community before the offender was released from supervision; and they must be considered high-risk at the end of their most recent period of supervision.

Vanderhoof met only the first benchmark.

Neither Douglas County’s parole office nor local police ever notified the community about Vanderhoof before he completed his parole. Oregon State Police don't put out any notices, and policies vary by county. Vanderhoof was considered low-risk at the end of his supervision, state records show.

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Briana Snow began a relationship with Vanderhoof in August 2010. Soon after, Snow’s close friend and neighbor -- identified as J.S. in the lawsuit -- had a bad feeling about Vanderhoof, her vigilance heightened by her own child’s sexual abuse by an intimate partner. The friend checked the public website for Vanderhoof, but didn’t find him on it, the suit alleges.

“If J.S. had found Vanderhoof listed on the predatory sex offender website, she would have told Snow, and Snow would have ended the relationship with Vanderhoof,’’ the lawsuit said.

Instead, Vanderhoof moved in with Snow within a month.

On Jan. 25, 2011, Snow was out of the house running errands when police say Vanderhoof violently assaulted her son. Vanderhoof called Snow, claiming the child had fallen from the porch. She found the boy unconscious, wet and unclothed at the foot of a bed and called 911. The boy died three days later at OHSU Hospital in Portland from a severe head injury.

A Douglas County judge last April found Vanderhoof responsible for causing the boy’s subdural hematoma and other injuries that led to his death.

Vanderhoof told detectives later that he shoved the boy to the ground for playing roughly with his pit bull.

“When I learned about Mark’s past, I couldn’t believe he wasn’t listed on the website,’’ Snow said. “It seems like that’s what the website should be for. If he would have been, this never would have happened, and Dennis would be still here. My goal for this whole thing has always been to make sure this doesn’t happen to someone else.’’

-- Maxine Bernstein