How many years in jail for third degree murder?

It depends on the state, Pa for example would give you life if found guilty

The death penalty in the majority of states, or life imprisonment in all states.

Sentences are case specific. In some states, first degree murder can be punished with death.

See: http://en.wikipedia.org/wiki/Rubin_Carter

This is just an estimation but, approximately 17,000 people are killed a year in the US. About 50% of those result in arrest, so probably around 8500 a year... and that doesn't include negligent...