izaak gillen of oregon was taken to randall children 's hospital on april 6 with the injury and was pronounced dead the following day .
detectives said he was at the babysitter 's house when he had skull fracture .
medical examiner determined child 's manner of death was a homicide .
parents justin and stacy gillen said they are deeply saddened by the loss .
no arrests have been made and investigators are still looking into incident .