CHESAPEAKE, Va. (AP) — Lee Boyd Malvo was strong-willed and hot-tempered but not mentally ill during last year's Washington-area sniper spree, a psychologist for the prosecution testified Monday.

The testimony contradicts defense witnesses who have described a malleable Malvo vulnerable to brainwashing by sniper mastermind John Allen Muhammad and unable to tell right from wrong during the killing rampage.

Psychologist Stanton Samenow, who interviewed Malvo eight times last month, said Malvo described himself as strong-willed and emotionless. "He said, `I wouldn't want to be anyone else. I'm not impressionable. I'm not weak-minded,"' Samenow said.

He agreed with Malvo's self-assessment, describing the 18-year-old defendant as "fully cognizant." He said he saw no evidence of mental illness.

"He did know right from wrong" on Oct. 14, 2002, when FBI analyst Linda Franklin was shot to death, Samenow said. Malvo is on trial on murder charges in Franklin's slaying and could get the death penalty.

"He was not operating under any irresistible impulse," the psychologist said.

On cross-examination, Samenow acknowledged that in more than 30 years of experience, he has never come across a criminal he believed was incapable of knowing right from wrong.

The statement "Criminals are readily able to discern the difference between right and wrong" appears as the "Concept of the Month" in November 2003 on Samenow's personal Web site.

Samenow also said he administered no psychiatric tests to Malvo, largely because he believes a patient can feign mental illness.

Malvo showed a strong will and a quick temper from an early age, Samenow said. He related an incident in which Malvo dawdled when he did not want to wash the dishes. The psychologist quoted him as saying: "I don't care if I get beaten till God comes home, I'm not going to do the dishes."

Malvo, 18, also related several instances in which he "snapped." Once he beat a schoolmate with a garbage can after discovering the boy had been stealing his lunches, the psychologist testified.

He told Samenow that he also once became angry with Muhammad when Muhammad said he had made Malvo into a monster. But Samenow said Malvo refused to discuss that incident in detail.

"People were afraid of his temper," Samenow said.

Muhammad was convicted last month for his role in the rampage that left 10 people dead. A jury recommended he get the death penalty.