Hi Silent Tears, I think it might be an idea to ask her (if you haven't already) if there have been any other times he has done this, and how she feels he treats her in general just in case there's more, and this isn't an isolated time.
If it's not an isolated time- then he is still hitting her, and if there's emotional abuse as well with yelling (??) then that is still abuse.
And if there are concerns, I know it might be difficult to get that far with it if he's a cop and a lawyer, but I'm thinking he wouldn't want it to get reported in the first place (to protect his reputation?). So maybe you could have a word with him and tell him that if it doesn't stop then you will have to report it to Child Services, perhaps that would help.
Although if there is a lot more to the story when you talk to your sister then you could go to Child Services anyway, they should have a legal requirement to act regardless.
But kudos on wanting to do right by your sister, which I think you are doing for her in terms of emotional support already.........by letting her know it isn't fair, it isn't her fault, that she deserves more, by comforting her, by being there for her.............
And maybe just encourage her to talk to you whenever anything happens that she doesn't feel is fair/right?? And as I'm sure you know anyway, it's really important to let her know that you believe what she's telling you.
And I am sorry he didn't give you the support you needed for your suicide attempts, if you're ever feeling you're in need of that kind of support then make sure you've got some helpline numbers, OK??
If he isn't going to help when you need him, there will be someone out there who will, don't let his dismissal of you hold you back from getting the support you need from elsewhere.

Alison