On day three of his murder trial, Mark Vanderhoof’s criminal past came back to haunt him, as the prosecution sought to show his alleged victim’s death wasn’t an isolated accident. An ex-girlfriend testified that Vanderhoof beat and tortured her and her 4-year-old daughter in 1985. Vanderhoof, 53, is charged with murder and murder by abuse in the 2011 death of a 2-year-old, Dennis Young, who suffered fatal head injuries. The Lookingglass man told detectives he angrily pushed the boy down because the toddler was playing roughly with Vanderhoof’s pit bull. The woman spoke calmly on the witness stand as she …