They should have charged him with manslaughter but maybe jury can still go down to that? manslaughter has way less intent when it comes to proving it. I think the DA made a mistake and caved to media pressure in making it a murder case. The g/f being illiterate and snarky, caught in some small lies and wasn't really an outstanding witness. Not bad but not great either.
This is one of those cases the DA probably wishes it didn't have to try.