so what is different in those cases and the one of Martin shooting the burglars?
The difference is, Martin fired at men who were running away.
He used an illegally held shotgun (he had his shotgun licence revoked for shooting at a man and boy stealing apples from one of his trees)
He had told people prior to the even that he would kill the next person to break in.
He had laid various traps around the house.
He had told police investigating a previous burglary that he would like to get all the local gypsies, put them in one of his fields, and machine gun them.
Martin didn't even report the incident to police, it was only when one of the wounded burlars turned up at a house seeking medical attention that the police were called.
Martin had gone out, hidden the shotgun, and checked into a hotel, all without calling the police.
Above all, though, Martin lied throughout. His version of what happened did not fit in with the forensic evidence.
He claimed to have only fired from halfway down the stairs, he said he was too frightened to go further. However, 2 of the 3 shots he fired hit walls as well the burglars, and the places they hit were not visible from any point of the stairs.
The fact that Martin shot 2 men in the back, didn't report it to the police, and in fact fled the scene, lied about the events, had previously announced his intention to kill, and had set traps around his house and garden, convinced the jury that he wasn't acting in self defence.
A lot of the "facts" people believe about the Martin case are not facts at all. Two weeks after he shot the burglars, Martin hired Max Clifford, a "publicist" who specialises in sleaze and media manipulation (he also represented OJ Simpson).