A 20-year-old man who allegedly sexually assaulted two young girls in Newbury, one of them on videotape, is incompetent to stand trial because he talks only to children, not adults, and therefore can't consult with his lawyer, a judge ruled yesterday.

But Robert Derderian, who experts believe suffers from autism or selective mutism and possibly Asperger's syndrome, will be evaluated for involuntary commitment to the state hospital because he poses a danger to others, Judge Carol Ann Conboy said.

If treatment there eventually makes him capable of participating in his own defense, he could still face criminal charges.

Derderian has never spoken to his public defender, Tracy Scavarelli, and did not speak in court yesterday. As Conboy issued her order, he held his head in his hands. Derderian was taken from the courtroom in handcuffs to the Merrimack County jail, where he will be held for up to 90 days for evaluation.

State prosecutors intend to file a petition to have Derderian committed within those 90 days, said George Waldron of the Merrimack County Attorney's Office.

It's a case that has taken more than two years to partially resolve.

Derderian, then of 25 Washington St. in Newbury, was charged in February 2007 with six counts of sexual assault against a 12-year-old girl, according to court indictments. He was also given child pornography charges for having a video of one of the assaults, the records said.

It was that video that tipped the Newbury police to the alleged assault. In late 2006, one of Derderian's friends told them Derderian had shown him that video, launching the investigation, according to a police affidavit.

When news of those charges appeared in the newspaper, another girl, who was 10, told the police she too had been sexually assaulted by Derderian, according to the police. Derderian was charged in April 2007 with sexual assault and indecent exposure against her.

Derderian's "severe mental disabilities/impairments" have been an issue from the beginning when a judge noted them in an order granting Derderian bail. They've also been an ongoing point of contention between the prosecution and the defense.

Dr. James Adams, a psychiatrist, evaluated Derderian for the state and concluded Derderian has "selective mutism," a condition Adams described as a willful decision not to communicate with adults. According to court records, he believed Derderian could consult with his attorney, a requirement to stand trial, "but chooses not to."

The condition is a rare childhood anxiety disorder that improves, and can vanish, as children grow up and are forced to deal with the outside world, Adams said. With treatment, medication and a move from his parents' home to an adult environment, Adams said, Derderian could be "restored" to stand trial.

According to court records, the defense's expert, Dr. Philip Kinsler, a psychologist, agreed Derderian could be treated and eventually work with his attorney for trial. But he said Derderian suffers from "autism spectrum disorder" and possibly Asperger's, court records said.

That means Derderian lives with a "crippling anxiety" about interacting with adults, Kinsler said, and was unable, not unwilling, to speak with them. But like Adams, Kinsler recommended Derderian leave his parents' home and go to a group home that specializes in treatment of "sexual misbehaviors," according to court records.

After hearing those opinions at a court hearing a year ago, Conboy concluded Derderian was incompetent to stand trial but could be restored with treatment. She gave Derderian 45 days to leave his parents' home for another supervised adult environment, and she told both parties she would revisit competency in a year.

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