Lee Boyd Malvo (search) 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. A second psychologist also said Malvo had no mental illness.

Their testimony contradicts defense witnesses who have described a malleable, obedient Malvo vulnerable to brainwashing by sniper mastermind John Allen Muhammad (search) 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 independent 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 (search) 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.

Later Monday, psychologist Evan Nelson testified that Muhammad "had a tremendous influence on this young person, absolutely." But he defined it as idol worship, instead of brainwashing as the defense argued.

Nelson added that Malvo's behavior, which included meticulous planning of the killings "is the antithesis of someone who cannot control his impulses."

The prosecution rested its case after Nelson's testimony. On Tuesday, the lawyers and Circuit Judge Jane Marum Roush will work out jury instructions. Roush estimated the jury will hear closing statements Tuesday afternoon, after which they would begin deliberations.

Earlier Monday, Samenow testified that Malvo showed a strong will and a quick temper from an early age. Malvo once beat a schoolmate with a garbage can after discovering the boy had been stealing his lunches, the psychologist testified.

Malvo 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.