What can I do about my brother who has POA if he takes our mother's property when he wants?

A gift was given, a small lamp for a Christmas gift several years ago to my mother. I, her daughter, was told to pack the things she wanted to give to her children and grandchildren. I did what she said. I was told to put everything in one room and lock the door. Now my mother is going to a nursing home. It was not her choice but my brother's. Brother broke into the locked room, went through some boxes looking for that "lamp". He never said anything to my mother about doing so. My mother is blind, brother and wife have been going in and taking what they want! That's stealing! I want to know what can be done. I live in another state. One brother is the executor, the one brother, the one that's stealing, is the power of attorney.