Chesapeake, Va. -- The experts have likened him to a child soldier and cult member. They said he was clinically depressed, even suicidal. They concluded he had lost touch with his identity and could not differentiate right from wrong. But was Lee Malvo, the younger defendant in the sniper attacks in the Washington area, legally insane when he took part in the rampage?
A host of mental health experts for the defense have offered evidence that he was, asserting that Mr. Malvo was effectively brainwashed by John A. Muhammad, the convicted mastermind of the killings, into participating in the shootings.
By trying to equate brainwashing with mental illness, Mr. Malvo's lawyers have pushed the boundaries of the insanity defense into a gray area where precedents are few and obstacles to winning an acquittal are high, legal experts said.
"They are between a rock and hard place," said Christopher Slobogin, an expert in mental health law at the Levin School of Law at the University of Florida in Gainesville. "It has traditionally required a serious mental illness such as psychosis or serious personality disorder to prove insanity. It doesn't appear he has either."
But even if the defense fails to gain an acquittal, it would score a victory if the jury is moved to sympathize with the defendant, experts said. That sympathy might cause jurors to recommend a life sentence instead of death if Mr. Malvo is found guilty and the trial moves to a penalty phase.
"At a minimum, I'm sure the defense has moved the jury from a sense of outrage about the random killings to asking, `Who is Lee Malvo?' " said Scott Sundby, an expert on the death penalty at the Washington and Lee Law School in Lexington.
Mr. Malvo is on trial in the killing of Linda Franklin, an F.B.I. analyst, in October 2002 outside a Home Depot store in Falls Church. Mr. Muhammad was convicted in a different killing and sentenced to death last month by a jury in Virginia Beach.
Mr. Malvo's lawyers are expected to rest their case on Thursday.
Winning an insanity case requires convincing jurors that a defendant was unable to distinguish right from wrong because of a severe mental disease or impairment. Juries have historically been somewhat skeptical about the plea, experts said. But they have been willing to accept when defendants were shown to suffer from serious problems like hallucinations, amnesia, multiple personalities or unshakable delusions.
Mr. Malvo's lawyers have not shown that kind of disorder. They have argued that he was mentally ill as a result of brainwashing by Mr. Muhammad.
Mental health experts for the defense have likened Mr. Malvo's relationship with the older man to the ties a a cult member has to a charismatic leader or a child soldier to a warlord. A result, they said, is that Mr. Malvo lost all sense of morality, all sense of identity, and became little more than an extension of Mr. Muhammad ego.
Exploiting Mr. Malvo's hunger for a father figure, Mr. Muhammad trained Mr. Malvo to be a soldier "in his war against America," Dr. Neil Blumberg, a forensic psychiatrist from Maryland, testified on Wednesday.
Mr. Muhammad used an array of techniques to indoctrinate Mr. Malvo, Dr. Blumberg and other experts testified, including isolating him, controlling his diet and sleep, forcing him to watch violent videos, training him to use guns and teaching him a violent brand of Islam and black separatism. The indoctrination desensitized Mr. Malvo to violence, broke down his already shaky sense of self and made him unable to resist Mr. Muhammad's commands. In psychiatric terms, the experts said, he suffered from dissociative disorder.
"He doesn't have multiple personalities," Dr. Blumberg testified. "But he's lost his sense of identity as a result of the prolonged and coercive persuasion or indoctrination."
The prosecutors have raised several questions about the defense case. They have argued that Mr. Malvo voluntarily chose to be with Mr. Muhammad, that the so-called indoctrination lasted just a few weeks and could not have completely impaired his faculties and that he was predisposed toward antisocial behavior.
The prosecution has also seized on the fact that Mr. Malvo has on several occasions expressed revulsion or reservations about Mr. Muhammad's violent plans - once even attempting suicide to avoid killing people - as evidence that he knew that those plans were horribly wrong.