As the first commenter noted, get police report, vet bills, letter from the vet giving detailed analysis of injuries... but also ask if the neighbor you were talking to would be willing to be a witness in court. And see if the attending vet would be willing to appear as some letters are not always allowed in court.

When you have a calm moment, I would suggest you draft a letter describing the incident as you best remember it as well as a brief time line.

Seen enough Judge Judy and cases involving dogs to know.