How can you tell if someone is going to kill someone else?

My parents are going to get divorced. (They are separated now). There's money issues right now. my dad has moved out into an apartment and isn't helping to pay for any of the bills. He just found out that we r in debt and we owe more on the house than he thinks. I am soooooooo afraid he is going to hurt/kill my mom. He still has access to our house. Of course, he would never do anything to hurt me or my sister (his kids), but I'm afraid he will get so mad that he will kill her. How can I tell? He says he would never lay a hand on me, my sister, or my mom. And they need to work things out. But, I'm still scared he is going to hurt her. I'm really paranoid. What can I do?