The fact that he had a gun is neither here nor there. He could have killed him with an icecream scoop, what difference does that make?

He defended himself and his property. He'd been robbed many many times before and the Police were sod-all help. He was at the end of his tether and desperate. When faced with a scary situation, he responded.

He has shown regret that the situation arose, but not that he killed him. Quite right, see above.

Your points...

1) True. But it was not murder, and he should be paroled by now. The only reason he's not been paroled is because he hasn't said sorry. Why should that be?

2) See above, it makes no difference

3) He may have been wrong to kill him, but he should not be in prison now.

Yes, he should be on the streets.