My brother is not the man I thought he was. Trigger very long

My youngest brother (YB) and I have always had a good relationship. He was still in high school when our mother died. Our dad needed help caring for him and my grandmother who had demintia, so I left college to come home and help out. ( not a big sacrifice, I was leaving at the end of the semester anyway). I was proud of the young man he became. We had another brother (MB)who was in between us in age. As a family we enjoyed spending time together. (Trigger) Then we lost our brother to suicide (end trigger). Deacesed brother left behind a DD who was 1 at the time of his death (relavent later). When he died he left a insurance policy of $250,000 to my brother. Brother tells me he set up a trust fund for our niece and also set some aside for her college. I never had any reason not to believe it was true. My deacesed brothers bsc ex refused to let us see her. Here is the part dwil won't like, we used gpr to get visitation with his daughter. One of the things agreed to in the visitation order was we were never to tell dn anything about him, including his very existence. When our dad passed the visits of course ended. At this point dn was old enough to keep in touch on her own over the devil. Everything is fine until yesterday. DN started a group chat on Facebook and asked about her dad. I sent her some pictures and told her about him. She did not ask about his death and I didn't tell her. She had heard rumors about the life insurance, when she asked about it, YB was very evasive. I sent a text to YB and asked what was going on and found out he had spent every penny. I am broken hearted. Legally the money was his to do with as he pleased, morally he has stolen her money. I cannot in any way condone what he has done

I want to CO. So dwil, do I tell him why?

Tldr: brother stole $$ intended for niece, do I tell him why he is CO? Editied for clarification