LMG This is quiiite spooky! I have almost exactly the same past as you - had dd1 at 17, she's now 10, met my lovely dh when she was 3, now have dd2 who is 2.5 and got married 2 years ago. My exdp was not as bad as yours but pretty awful, and also has no contact. His sister also contacted me by facebook and i closed my account and reopened it in married name with settings on it that mean nobody can even click on my name unless i invite them I also had pnd, it was horrible. i look back on those days as dark dark times and i really totally understand why you would not want to go anywhere near him again. However, I think you have to support her with this cos otherwise it will build resentment between you and she needs you to be cool so she can have this wobbler and then recover.
Telling her he's dead is a bad idea. Sorry to other posters, I can see why it seems simpler but if she ever found out you'd lied it would harm her trust in you in such a massive way that it could never be worth it.
Regarding other children he may or may not have had, I suggest that you sit with her with some sort of family tree chart, fill in the bits you know, and show her how many other people you'd have to know to add on her half brothers or sisters. Put question marks there and explain that you have no way of knowing everyone he may have had children with, and that that aspect of it would be better and much easier to do when they are older and have their own facebook accounts etc and may also be trying to find out stuff about their heritage. You can't really go around asking people so she needs to know what is realistic. So you're not saying 'no' to her, you're saying it will take a long time to find out.
i'm waiting for the time when dd1 turns around and tells me that she wants to find him/relatives. She's not been fussed so far but I'm sure she will... So I'm really interested in your story....
I think that:
a) you should not open a facebook account cos he can hide behind it and she might build him up into something he's not. she would need to see him face to face to get it out of her system.
b) it would be really good to get counselling of some kind, for both of you even? because you went through some horrible stuff and this will be dragging it up for you, and you need to be in a strong place to help her through this phase. what about relate? don't they do this sort of thing as well? you might have to pay though, depending on your hubby's income...
c) she's old enough to see those pictures and hear it verified that he can be fine, but has also been aggressive and violent. that way you can explain to her why it will take a while, and why you need to be very careful how you get in touch with him. you can also tell her that there are certain rules to stick to to keep you both safe, and make a deal with her that if at any point you think either of you (or your dh and dd2) are in any danger you can back out and not look any further or have any further contact.
don't ever let him or anyone who knows him get hold of your address or phone number or anything. don't ever let him anywhere near you house, and if you intend to meet with him i think you should get some legal advice first and get a third party or meediator or something like that. take her with you to see the whole process cos it's important for her to know you're working on it but that it's complicated.
sorry this was so long... ii've had all this stuff in my head for years!!