Zimmerman hasn't confessed to anything. Self-defense is not murder.<quoted text>
"dumchit"??? How very Christian of you.
Anyhow, he's already confessed to 2nd degree murder. Its up to his defense to prove the extenuating circumstance of "self-defense". The prosecution doesn't have to prove a thing.
Juries are always instructed (at least here in California) that "the prosecution must prove the case beyond reasonable doubt." That places the onus on the prosecution to prove their version of events.