I don't buy that shit AT ALL.
An affair was jealous of another woman, but not his own fucking wife? You got to be kidding me. No mention of any alliby for the wife yet! Seriously, it's not hard to get powder residue on your hand, especially if you hold the gun in the G/F's hand (after she is dead) and use her finger to pull the trigger (might have been the last shot to the head).
I don't buy it at all, not for an instant.