In closing arguments Friday, a defense attorney and prosecutor agreed that exactly what happened to Dennis Young on Jan. 25, 2011, may never be known. This much was established during a four-day trial in Douglas County Circuit Court: Mark Vanderhoof was alone with the 2-year-old when the toddler suffered fatal head injuries. The defense and prosecution rested their cases Friday. Judge Ronald Poole is scheduled to render his verdict at 9:30 a.m. Tuesday in Courtroom 402. Vanderhoof, 53, of Lookingglass waived his right to a jury trial. He admitted to detectives he lost his temper and struck the boy, but …