Dozens of times during his testimony yesterday, the key witness in a homicide trial repeated the refrain "I was coached."

Recanting testimony given at a preliminary hearing and before a grand jury -- as well as statements to detectives -- the witness declared that neither defendant was responsible for a 2006 drive-by shooting in Homewood.

The 21-year-old witness, who prosecutors have asked not to be identified, testified that Joseph Hall, 19, of Penn Hills, and Lamont Hall, 20, of East Liberty, did not kill 17-year-old James Stubbs. The two defendants, whose case resumed Thursday after two mistrials, are not related.

Under direct examination from Daniel Fitzsimmons, chief trial deputy for the district attorney, the witness accused five different Pittsburgh homicide detectives of threatening and coercing him into implicating the Halls, who investigators had falsely assumed were the shooters.

"Today I'm not lying for detectives no more," the witness said. "Whatever I say now is the truth, believe it or not."

The witness could face perjury charges for changing his story under oath.

The tale he gave yesterday began when he and Lamont Hall drove to Westinghouse High School to pick up girls as school was letting out. The witness said neither of them was armed, nor were they looking for trouble.

The witness said as he was driving down North Lang Avenue he saw about five people shooting at one another from opposite sides of the street. The witness said he panicked and sped away from the scene and only met up with Joseph Hall afterward.

Later, the witness testified, when he heard that someone was killed in the area, he feared someone might describe his car to police and he would be unjustly blamed for the shooting. So the witness made a false report to authorities, saying his car had been stolen, but he had found it a short while later.

In interviews with detectives that night and a few days later, the witness testified, he was told what to say. If he didn't comply with the detectives' written script, they would rewind the tape and ask him to record another statement.

He said detectives didn't read him his rights, threatened him with a 20-year conspiracy sentence, and coerced him with pizza and cigarettes.

"I kept trying to tell them what happened, but they weren't hearing me," the witness said. "I don't know anything about the law, rights, justice. I just did what they told me to do."

The witness made similar statements about the Halls' innocence in two videotapes, played for the court yesterday, that he made with the mothers of the defendants in late 2007.

But in January 2008, the witness testified under oath at a grand jury proceeding that both Halls were shooting from his car.

Jurors also heard two recorded statements the witness made to detectives, including specifics about the guns used by the defendants and Joseph Hall's celebration when he heard Mr. Stubbs had been killed.

"That's a story they fed to you line by line, word by word. Is that what you're saying?" Mr. Fitzsimmons asked the witness.

"Yes sir," he responded.

Sprinkled with hostile exchanges, the testimony took nearly the entire day and is scheduled to continue tomorrow, with Mr. Fitzsimmons resuming his direct examination.

In his opening statement, Mr. Fitzsimmons indicated that he does not have physical evidence or other witnesses to link the Halls to the shooting.