Testimony began yesterday in the trial of two teenagers charged with slaying a high school student in 2006 near Lincoln Intermediate School in Homewood.

Joseph Hall, 18, of Penn Hills, and Lamont Hall, 19, of East Liberty, who are not related, are on trial for the death of James Stubbs, 17, a student at the city's Student Achievement Center, who police believe was shot while walking home from school.

Mr. Stubbs, of Homewood, died of a single .22-caliber bullet wound to the back.

The key prosecution witness initially told police his car was stolen. He later admitted the two Halls were riding in his car at the time of the homicide. He said as he was driving, both defendants were firing guns at people or objects outside the car and people outside the car were firing back at them.

The witness made a different statement at a preliminary hearing, where the prosecution alleges he had contact with Joseph Hall's mother. The witness then showed up at the mother's work place and he agreed to film two videos in which he reportedly claims that the Halls had nothing to do with the shooting.

Police never found the .22-caliber gun believed to have been the murder weapon.

"You're not going to have ... a CSI moment in this case," Daniel E. Fitzsimmons, chief trial deputy for the Allegheny County district attorney, told jurors. He asked the jury to convict both men of first-degree homicide, criminal conspiracy and possession of firearms without a license.

Attorney T. Brent McCune, who represents Joseph Hall, asked the jury to focus on the key witness: "This man has given such widely different versions that who knows what he's going to say?"

Elliot Howsie Jr., attorney for Lamont Hall, said despite the "variety of statements" from the key witness, "the one thing that is consistent is that Lamont Hall didn't shoot anyone, he didn't aim at anyone, he didn't kill anyone and he didn't conspire with anyone."