I'm so sorry for what you are going through, I am going through a similar situation myself, I lost my little Lola a week and a half ago from a pit bull attack, it is horrible.
I do suggest going to the police and filing a report so no other dogs have to suffer the same awful fate. We did and had to go to a hearing and are still awaiting the decision as to what is going to be done about the pit, but it is very important to get vicious animals off the streets and keep them safe for our furbabies.
I know nothing we can say or do can take away the pain you are feeling now, as I still feel that same pain, but please take comfort in the memories and love that your little one gave you.
RIP Ana