Some suggestions would be nice. (deck theft)

So my little brothers entire deck box got stolen last week. Contents were a fully blinged-out Inzektor deck (tour guides, high rarity staples, zenmaines) and a Hieratic deck (Atums, Card Car D's, etc). I normally wouldn't include that part but I wanted to emphasize how much he lost and how upset we both kind of are.

Anyways, today I was given the identity of the suspected person (he only comes on the weekends) and was told to outright confront him by my brother. Sounds kind of stupid, seeing as he would probably outright deny it but it was what my brother asked of me. Sure enough, he denies it and I see no trace of it in his binder. I had to go out for a date later that day but it turns out him and someone else made a huge transaction using his cards when I was absent (I asked some of the other guys to message me if they saw anything while I was out).

So needless to say, I'm feeling kind of shitty that I couldn't help more. Was going to write something else but forgot. Suggestions pl0x.

TLDR; brothers deck stolen. confront suspected thief. thief denies. thief's identity confirmed when i am absent with no solid evidence. suggestions.