Chesapeake, Virginia -- Teenage sniper suspect Lee Boyd Malvo "displayed a pathological loyalty" to John Allen Muhammad and was so brainwashed by him that he no longer knew right from wrong, a defence psychiatrist testified Wednesday.
Malvo "was merged with Mr Muhammad," Diane Schetky said at Malvo's capital murder trial. "He was acting as his proxy. He was like a puppet in his hands."
Malvo, 18, and Muhammad, 42, are accused of carrying out a three-week sniper rampage that killed 10 people in the Washington DC area last year. Malvo is on trial for one of the killings - that of FBI analyst Linda Franklin - and faces the death penalty if convicted.
Asked by defence lawyer Craig Cooley if Malvo was able to distinguish right from wrong - the legal standard for insanity in Virginia - Schetky said, "I believe he was not."
Schetky was the second defence witness to diagnose Malvo with a dissociative disorder, a mental illness that involves a distorted view of reality.
Malvo's attorneys are mounting an insanity defence.
Schetky said Malvo "displayed a pathological loyalty to Muhammad" and confessed to being the triggerman in the killings when police suggested that the shooter would be the one who took the rap for the crimes.
Malvo has since recanted his confession and said Muhammad was the triggerman in nearly all of the shootings.
On cross-examination, Schetky said she didn't question Malvo extensively about his specific behaviour during the sniper shootings, saying his responses to such questions were robotic and provided little insight.
She also said Malvo felt conflicted about the October 7, 2002, shooting of 13-year-old Iran Brown outside a school in Bowie, Maryland. He thought killing children "was very wrong ... but he was complying with the plan." She said he was "relieved the shot did not kill him".
As Malvo trained for the sniper spree, Muhammad taught him that emotions were the enemy and should never be allowed to interfere with his paramilitary mission, Schetky said Tuesday.
Muhammad told Malvo that "if his conscience was bothering him, he should lock it up in a box and throw away the key," she said.
Schetky also said Muhammad convinced Malvo that "right and wrong" are artificial constructions that have no real meaning.
Prosecutors argued on Tuesday that Malvo was a willing participant, noting that he twice ran away twice from his mother and chose to be with Muhammad.
Prosecutor Robert Horan said Malvo committed his first killing about 10 weeks after he first ran away - the Febuary 16, 2002, slaying of Keenya Cook in Tacoma, Washington. Malvo has admitted walking up to Cook's house and shooting her in the face at point-blank range.
Prosecutors are expected to put on their own mental-health expert, who has been meeting with Malvo since before the trial started on November 10.