Rockville, Md. ? John Allen Muhammad was convicted of six of the Washington-area sniper killings Tuesday after the prosecution’s star witness, Muhammad’s young protege, portrayed him as the mastermind of an audacious terror scheme in which phase two would have been bombings against children.

Muhammad, 45, is already under a death sentence in Virginia for a killing there. The most he can get for the six murders committed in Maryland is life in prison without parole.

The jury took slightly more than four hours to convict him after a four-week trial in which he acted as his own attorney.

Ten people in all were killed and three were wounded in Virginia, Maryland and Washington, D.C., in the string of shootings that gripped the metropolitan area with fear.

The trial marked the first time Lee Boyd Malvo testified against the man prosecutors say was his mentor and manipulator. And Muhammad’s cross-examination of Malvo marked one of the most dramatic moments.

According to Malvo, Muhammad had a two-phase plan – six shootings a day for a month, followed by a wave of bombings of schools, school buses and children’s hospitals. Malvo said that when he asked Muhammad why, the older man replied: “For the sheer terror of it – the worst thing you can do to people is aim at their children.”

Muhammad hoped to extort $10 million from authorities and use the money to set up a school in Canada to teach homeless children how to use guns and explosives and use violence to shut down other cities, Malvo said.