 Cregan had earlier pleaded not guilty to the murders of PC Nicola Hughes and PC Fiona Bone, and the murders of Mark Short and David Short, in an appearance by video link at Liverpool Crown Court.Cregan changed his plea to guilty for the murders of the two police officers on 12 February 2013, and pleaded guilty on 22 May 2013 to the murders of father and son David and Mark Short.The killings of David and Mark Short were the culmination of a decade-long feud between two criminal families in Manchester, the Shorts and the Atkinsons, with whom Cregan was friendly.