They really have turned Chas into a despicable character, she will not accept any blame for the situation. Nobody seems to notice that she is constantly going out to get "some fresh air". She obviously has no feelings for Paddy, how long before she blames him for what's happened?
Cain could put up a better defense, if he said he was in barn and Al came in and started a fight, and that during the course of this Al grabbed the gun and it went off killing Al, then Cain could claim he was not to blame for any of it.
I wonder if Kerry has noticed that Al left his keys before leaving the house.