BIL(22/M) stole cousin’s wedding jewellery but still acts kind. how do I handle trust?

My brother in law (22/M) has always come across as kind, respectful, helpful, and well liked over the 10 years I’ve known him.

Last year, my husband found out he had stolen the wedding jewellery of their cousin (worth around 500k) and sold it for about half the value to buy gadgets. He initially denied it, then admitted when proof was found. He also admitted to stealing from his own mother before(She was safekeeping inheritance money which was to be given to charity and a significant aum went missing). Neither he nor my MIL knows that I’m aware of this, my husband told me privately.

What makes it harder to process is that when the jewellery first went missing, he actively helped search for it. The cousin initially suspected her husband, which worsened their already strained relationship and contributed to their divorce. The husband is now widely disliked, and my BIL supported her and spoke against him.

Most of the family/cousin still doesn’t know the truth. My MIL plans to compensate the cousin in the future. Around the same time, my BIL was also suspended from college for ragging. He has since finished college and is now interning under that same cousin.

On my side, I’ve had things go missing too, including a gold chain when I was away. I used to think I misplaced it, but now I’m unsure.

The confusing part is that he still behaves like the same gentle, helpful person.

So I’m struggling to understand: is this manipulation, a “mask,” or someone who made serious mistakes? And practically, how do I handle trust here? is he even guilty of his actions? if so how can he work with the person he wronged without feeling even an ounce of guilt?

TLDR:

BIL who seemed kind stole cousin’s wedding jewellery, denied it, then admitted it. Even helped search at the time. Situation led to major family fallout. I’ve also had items go missing. He still behaves normally. Unsure how to understand him or whether to trust him.