kingsley burrell , 29 , arrested by police and sectioned on march 27 , 2011 .
mr burrell had called officers , alleging three men put a gun to his head .
but cctv later showed nobody approached him , so he was hospitalised .
four days later he died in custody , and allegedly told family about ordeal .
court told that police allegedly beat mr burrell , restrained him for six hours , and forced him to wet himself by denying him access to a toilet .