Need help in forming a case against domestic animal abuser

Hello, this is my first post to a forum like this so please disregard any format errors.

As the title reads I need some of guidance forming a case of domestic animal abuse that escalated to the death of 5 animals and critical neglect of 4 other animals.

I have tried reaching out to my local humane society (where a few of these pets were adopted from) about the abuse and was redirected to contact my local authorities since it falls out of their jurisdiction. I am worried about going to my local authorities and not having enough information/ being turned away as it has been 3-4 years since the abuse took place, making evidence like autopsies hard to provide.

I am a first hand witness to the animal abuse and lived in the same household as these animals, but I do not know if my word alone will be sufficient. I would also like to stay anonymous as the abuser is also violent towards people (I was previously assaulted by them and moved out due to fear of consistent abuse).

The hard evidence I have are records from visits to the vet for treatment of FIP for one cat, cremation records for another pet, and search efforts for a pet that ran away from the home. Search efforts were organized by the local humane society and Petco Lost Love.

The neglect escalated quite fast after I moved out of the apartment along with more pets being adopted. Many animals were left in unkept shelters with feces and urination. Animals left inside of unconventional enclosures such as closets. Food infested with bugs and animals left without sufficient water supply. Animals fighting with one another leading to the death of another pet.

Again, I am wondering whether this is worth building a case on as the abuse was scattered over the time of a year and a half (2021-2022)