There is a requirement or facts to fulfill for the said "self-defense" and ofcourse If the requirement was fulfilled on the 78 yrs old pensioner could not be going to jail and actually it's the job of the police to find the facts of self defense for the defendant. But on the on the hand we know it was not moral good to take lives someone but what if the 78 yr old was the one who killed? then intruder lives? Think again.