You have a tough case. First, you would have to figure out who this owner is. Second, in Texas, you have to prove the owner the dog is vicious and the owner had knowledge or constructive notice of that fact. See Lewis v. Great Southwestern Corporation, 473 S.W.2d 228 (Tex. Civ. App.-Fort Worth 1971, writ ref'd n. r. e.),
Pretty hard to do. Contact a private investigator. Comb the neighborhood looking for other witnesses who may know the person. There are no magic tricks unless the person has a highly unusual first name.
This is not to be construed as legal advice. I do not have an attorney client relationship with you.