A former Peabody police officer once charged with beating his mother unconscious will not get his job back, after the state Civil Service Commission denied George Sideris’ appeal for reinstatement. Sideris was accused of beating his elderly mother on Thanksgiving Day 2004. Although he admitted the beating, the case was eventually dismissed because of mental health and competency issues that made it impossible for him to stand trial. The lack of a conviction prompted Sideris to ask for his job back. The Salem News reported that the commission ruled that due to Sideris’ ‘‘lengthy, involuntary commitment due to delusional disorder’’ as well as questions about his ability to legally own a gun he should not get his job back.