Convicted Washington-area sniper John Allen Muhammad should never have been allowed to act as his own lawyer for part of his 2003 capital murder trial, his attorney said Tuesday in a federal appeals hearing.

Muhammad's conviction and death sentence should be thrown out because his trial lawyers failed to tell a judge that the mastermind of the 2002 shootings was too mentally impaired to represent himself, attorney Jonathan Sheldon said.

A lawyer for the state of Virginia argued Muhammad's competency was never an issue in his trial for one of 10 killings committed by Muhammad and teenage accomplice Lee Boyd Malvo. Muhammad was sentenced to death, and Malvo is serving a life term for the shooting spree.

Muhammad represented himself for the first two days of his Virginia trial, making his own opening statement and questioning 18 witnesses before turning his defense over to court-appointed attorneys.

Sheldon, who is handling Muhammad's federal appeal, said the trial lawyers violated Muhammad's constitutional right to effective counsel by not telling the judge about their client's delusional statements and brain disorders stemming from childhood beatings.

"They had an absolute obligation under state law to hold a competency hearing," Sheldon told a three-judge panel of the 4th U.S. Circuit Court of Appeals.

Katherine Burnett, the state's senior assistant attorney general, his attorneys in the Virginia case did their duty in discouraging him from representing himself.

U.S. District Judge Liam O'Grady ruled last year that there was no evidence Muhammad was incompetent and unable to represent himself in his trial for the murder of Dean Meyers.

In all, 10 people were killed were in four states and the District of Columbia during a rampage that terrified residents of the region. Six people also were wounded.