I feel so sorry for this 78 year-old man.
Just imagine - being confronted by two young men, in your own home, in the middle of the night. He must have been terrified!
And then, to have one of them threaten him with a screwdriver, whilst the other was upstairs, ransacking his home, and perhaps hurting his wife ...?
He was very brave to defend himself (and his wife). He probably reacted instinctively with the knife, and wouldn't be thinking about actually killing the burglar, just wanting to get rid of him.
MawBroon is right. There's no way this is murder!
And just think how that man must be feeling now. He will be shaken (to say the very least!). Traumatised by the event! He's killed someone, been arrested for murder ... I doubt he will ever get over it. (A twenty year-old would have trouble getting over it!)
I applaud his courage and strength, and hope that it holds him up during this awful time.
As for the burglar - wrong time, wrong place ...