A Thunder Bay police officer is not guilty of assaulting a 12-year old boy. The three-day trial of constable Steven Oster concluded Wednesday with the not guilty verdict. The incident took place in January of 2013 during a minor hockey tournament at the Neebing Arena. The judge ruled that the Crown failed to prove beyond a reasonable doubt there was a criminal assault. The 43-year old Oster had been on administrative duty since the charges were laid.