Daniel Bark of Toms River, N.J., was arrested Sunday evening and held on $35,000 bail on charges of reckless driving and leaving the scene of an accident -- charges that could land him in jail for 10 to 15 years if convicted.
Cops said Cohen's death was the result of vehicular homicide.
Deputy Chief Michael Mohel of the Ocean County Prosecutors Office says an autopsy indicated she suffered chest, head and abdominal injuries caused by the collision.
A passing driver noticed Cohen and called 911. FirstAid workers rushed her to a nearby hospital, but it was too late.
Cops found Cohen's car parked in a lot about 300 yards away from where her body was found.
Cohen auditioned in Philadelphia for the popular Fox singing competition in August 2007 and the episode was aired in January 2008. In it, she said, "I march to the beat of a different drummer."
She was best known for her angry tirade about being rejected by "American Idol" judges, a flare-up that went viral online. The video quickly became a YouTube sensation.
The aspiring performer tried out again during the show's eighth season, but again failed to make it to the second round.