As far as I know the police have to make the arrest "on suspicion of" while investigations are underway/complete.This pensioner killed the burglar[allegedly a career criminal who targeted pensioners]in his home-kitchen I believe-while his wife was held in another room.If this is the truth of the matter then even if a trial ensues I reckon he'd get a not guilty verdict.Tony Martin was different as he shot someone in the back as he was running away and was outside the home,not saying he was wrong to do so,but it's different circumstances and I'd think comes under "reasonable force" or "fear for life".If you don't want to get killed or injured whilst burgling someone then don't do the burglary in the first place.