BOSTON - The question for jurors won't be whether Joseph Druce killed convicted pedophile priest John Geoghan, who was beaten and strangled in his prison cell, but whether he should be held criminally responsible. Prison officials said they found Druce inside Geoghan's cell, with the door jammed shut so no one else could enter, and that Druce bragged openly about killing "the child molester" and told investigators he did it to "save the children." With jury selection due to begin Monday, Druce's lawyer, John LaChance, plans to use an insanity defense. He argued during pretrial hearings that Druce was suffering from a "major mental illness." Druce, a convicted murderer who already is serving a life sentence, has been hospitalized at least twice for ingesting foreign objects. In September 2003, just two weeks after Geoghan was killed, Druce swallowed pieces of a pencil. Three months ago, he swallowed a piece of television cable and a piece of his eyeglasses. Druce, 40, unsuccessfully used an insanity defense during his 1989 trial for the killing of a man who allegedly made a sexual advance toward him after picking him up hitchhiking. According to psychiatric testimony at that trial, Druce was a troubled child with violent fantasies. Records introduced at the trial showed he took the anti-psychotic drug Thorazine and the hyperactivity treatment Ritalin as a teenager. Druce claimed he had been sexually abused when he was a child. Geoghan's case sparked the clergy sex abuse scandal that erupted in Boston in 2002 when records were released showing that church higher-ups had shuffled him and dozens of other priests from parish to parish despite allegations they were sexually abusing children. Other defense attorneys who have used the insanity defense said that no matter how much psychiatric evidence Druce's lawyer might produce, it might not be enough to persuade the jury to acquit him. "It's extremely difficult," said Boston attorney Joseph Balliro Sr., who argued unsuccessfully that Dr. Richard Sharpe, a cross-dressing dermatologist, was insane when he killed his wife with a hunting rifle in July 2000. "Inherent in a defense of insanity is that your client committed the crime. The second thing you're going up against is that you need (psychiatric) experts, and in criminal cases juries have the perception — whether it's accurate or not — that those are just hired guns," Balliro said. In addition, Massachusetts juries must be told by the judge that a defendant found not guilty by reason of insanity will be sent to a prison psychiatric hospital and could later be released. "Jurors are afraid that if they acquit by reason of insanity in a murder case, that they bear responsibility if he commits another homicide because they are not confident he will be held (permanently) in a maximum-security hospital," said J.W. Carney Jr., who used an insanity defense unsuccessfully in the case of gunman John C. Salvi III, who killed two people and wounded five others at two Brookline abortion clinics in 1994. Worcester District Attorney John Conte and Druce's lawyer did not return calls seeking comment before the trial. Geoghan, 68, was serving a nine- to 10-year sentence for groping a 10-year-old boy and also was accused in civil lawsuits of molesting nearly 150 boys over three decades. He was killed at the maximum-security Souza-Baranowski Correctional Center in Shirley on Aug. 23, 2003.