A Pennsylvania man was found guilty Saturday in the 2009 killings of three Pittsburgh police officers who responded to his mother's 911 call about an escalating argument.

The jury deliberated for just over three hours before returning the verdict against 24-year-old Richard Poplawski. He was found guilty of all 28 counts he faced. He was found guilty of first-degree murder in all three killings, the three most serious charges he faced.

About 50 Pittsburgh police officers lined the hallway outside Allegheny County Judge Jeffrey Manning's courtroom and burst into applause when Deputy District Attorney Mark Tranquilli emerged.

Poplawski did not comment as he was taken from the courtroom, and the judge ordered his mother, Margaret, removed as well after she stood up. Manning said he was concerned she was about to create an outburst and had sheriff's deputies remove her as a precaution.

As a result, Margaret Poplawski was not immediately available for comment after the verdict.

The trial now enters a penalty phase in which the jury will hear evidence about his mental state, background and other factors before determining if Poplawski gets the death penalty or life in prison without parole.