CHESAPEAKE, Virginia (AP) — Teenage sniper suspect Lee Boyd Malvo could have been vulnerable to brainwashing by sniper mastermind John Allen Muhammad because of a fractured childhood in which his mother often dropped out of his life, a cult expert testified yesterday.

“Instability is a factor in indoctrination,” said Paul Martin, a psychologist and former cult member himself. “People seek relief from that instability, that sense of insecurity in their life.”

Malvo’s lawyers are presenting an insanity defence in his capital murder trial, claiming Muhammad brainwashed their client to the point that Malvo could not tell right from wrong.

Malvo, 18, and Muhammad, 42, are suspected of carrying out a three-week sniper spree that left 10 people dead in and around Washington DC in October 2002.

Malvo is on trial for one of the killings — that of an FBI analyst. He could face the death penalty if convicted. Muhammad was convicted of another of the killings in a separate trial last month, and the jury recommended a death sentence.

The two also are suspected in shootings in Washington state, Arizona, Georgia, Alabama and Louisiana.

A series of witnesses testified earlier in Malvo’s trial that his mother, Una James, continually moved him from town to town and school to school as she traveled around the Caribbean looking for work.

Martin, who has never interviewed Muhammad or Malvo, offered general testimony on how brainwashing typically occurs, and answered hypothetical questions about how the circumstances of Malvo’s life apply in the context of indoctrination. He did not give an opinion on whether Malvo was brainwashed.

Prosecutors strongly objected to Martin’s testimony, saying he was not qualified to offer opinions on the relationship between Malvo and Muhammad.

Prosecutor Robert F Horan Jr argued that any testimony about indoctrination is irrelevant, because brainwashing is not a diagnosable mental illness that can lead to insanity.

“This specific testimony is designed to get the jury to think about things that have nothing to do with this case,” Horan said.

Circuit Judge Jane Marum Roush allowed the testimony but limited its scope.

The trial will begin its fifth week Monday with the testimony of Dewey Cornell, a clinical psychologist at the University of Virginia who was appointed by the court as the defense’s mental health expert.

Cornell’s presentation will include a 12-minute clip of the film “The Matrix”, as well as clips of violent video games that Malvo and Muhammad played together.

Social worker Carmeta Albarus testified Thursday about Malvo’s interest in “The Matrix,” in which the hero shoots his way out of a computer-imposed world of virtual reality.

There is no indication in Malvo’s case that “The Matrix” is a core issue of the insanity defence.