A 15-year-old Manassas youth who was slain over Father's Day weekend was apparently tortured before he was shot to death, witnesses said yesterday in Prince William County Circuit Court.

In the first day of the capital murder trial of Michael Carl George, 33, of Stafford County, a urologist testified that Alexander Eugene Sztanko had suffered injuries in his groin that could have been caused by electrical shock from a stun gun. The injuries below the surface of the skin apparently occurred while Sztanko was still alive because of evidence of bleeding, said James Sehn, a Manassas physician.

"I don't believe I've ever seen anything like this in typical practice," Sehn said. He later told the jury under questioning by Assistant Commonwealth Attorney James Willett that "these injuries would have been terribly painful."

Some in the crowded courtroom gasped when Willett turned on a battery-operated stun gun that was found when police searched George's car shortly after Sztanko's body was found on June 17. An autopsy determined that the youth had died of a single gunshot wound to the head.

During opening arguments yesterday, Commonwealth's Attorney Paul B. Ebert said the prosecution would present evidence to show that George killed Sztanko during a robbery, a capital offense. If convicted, he would be eligible for the death penalty. But defense attorney Lon Farris said in his opening arguments that it is unclear if a robbery occurred because Sztanko's wallet has not been found.

The trial, in which more than 50 witnesses may be called, is the first capital murder case this year in Prince William County. If George is convicted of capital murder, he would become the seventh inmate sentenced in Prince William County to Virginia's death row.

Atilla Stzanko, the youth's father, testified that he had last seen his son about 2 p.m. on Saturday, June 16, shortly after they had returned from the youth's grandmother's home, where he had mowed her lawn to earn money. The father testified that 30 to 60 minutes after his son rode his dirt bike into a utility right of way and recreation area known as the "power lines," he heard two shots from the area. The next day, the youth's body was found in the "power lines" near Interstate 95 and Cardinal Drive.

When George was arrested, police found a stun gun and a 9mm Beretta in his 1989 dark blue and silver Ford Bronco, authorities said. A medical expert testified yesterday that the fatal shot came from the Beretta. Also found in George's car were a large bow saw, a hacksaw and a machete, which were introduced into evidence.

Cpl. Joseph Scott Dillon testified that he arrested George on a trespassing charge about 11 a.m. June 17 after finding him walking near an area where police were searching for Sztanko.

Dillon said George was dressed in camouflage clothes and crouched to avoid detection when he saw the officer. A search of the woods near where George was walking turned up a pair of tennis shoes worn by Sztanko.

George spent 2 1/2 years in state prison after admitting in 1984 his involvement in the death of 8-year-old Larry Perry, who disappeared in the "power lines" near where Sztanko's body was found.