Good point...
He and Gabby lived with his parents. He moved Gabby's things from storage to his parents' house. So, when he returned to Gabby in Utah, his parents had Gabby's things in Florida. Then, when he returned to his parents' house in Florida without Gabby, both he and his parents had possession of Gabby's things.
He had control of any evidence, and so did his parents.
ran into a tidbit tonite may be important I think;
“I do believe that their relationship as they kept going on was getting more problematic. It just seemed like there was more and more arguments,” she told the Daily Mail, adding that they had still planned on getting married **despite Petito telling her mother it was called off.**
https://nypost.com/2021/09/17/brian-laundrie-was-controlling-had-episodes-gabby-petito-pal/