PITTSBURGH -- A judge who found a Pittsburgh-area oral surgeon not guilty on Wednesday of sexually assaulting or fondling 17 female patients while they were anesthetized had police escort him home and security outside his house overnight.

During the trial, Allegheny County Judge Anthony Mariani said he wouldn't be intimidated by an anonymous letter demanding a long prison term for Dr. Robert Boyda Jr., 44, of Mount Lebanon.

"I took the letter as a threat. The letter said that if I ruled a certain way that the person or persons who sent the letter would have a problem with me," Mariani said.

The letter, mailed from Chicago, purports to be from 500 people who had attended dental school with Boyda at Northwestern University. It said that Boyda had a history of behavior that was similar to the charges he faces now.

The letter said if Boyda isn't convicted, its senders will be angry at the judge, not at Boyda.

Mariani contacted the FBI and they were in the courtroom for Wednesday's verdict.

"There was one FBI agent and there were other members of law enforcement there as well that were in plain clothes...Certainly you have to be prudent about this. I rendered a decision. It was not the decisioon that the letter was advocating," Mariani said.

Mariani said he believes the women thought they were assaulted by Boyda, but that defense experts raised doubts because the women had been given so many drugs, including one that can cause sexual hallucinations.

Mariani said his verdict might be different had the case been heard in civil court, where the burden of proof is lower.

Defense attorney William Difenderfer said Boyda wants to resume his practice and plans to videotape procedures.