MINEOLA - An expert witness who had previously testified for the prosecution in Evan Potts' deadly road-rage trial took the stand for the defense today.Potts, 22, is accused of running down 34-year-old Ian Sharrin with his Nissan Altima in Long Beach in 2009.Police say Potts told them Sharrin pursued him for nearly 2 miles after Potts cut him off. According to Potts' father, Ray, Sharrin "wasn't going to stop until he got his pound of flesh."Today, Dr. Timothy Roberts, formerly a witness for the prosecution, testified that Sharrin's post-mortem urine tested positive for high levels of steroids. "The test really puts the stamp of approval on what Evan told the police hours after the accident happened," says Potts' attorney, Stanley R. Kopilow. "He said, 'Look, I was in a panic, I was trapped, I was trying to get away from a guy who was crazy.'"The prosecution, however, calls the testimony irrelevant, saying it doesn't excuse Potts's actions. Sharrin's family denied that the 34-year-old used steroids.