My mom is dating a murderer: Advice?

My mom went through a nasty divorce two years ago to a man she was married to for nine years. About a year later, she started dating a man who just got out of prison ( she also has a criminal record and was in prison before). She works for drug rehabilitation and helps people who just got out. Anyways come to find out this man is a murderer. She never said anything to my husband or me before bringing him around our children. So I finally had to step up to her and tell her it makes me uncomfortable. My mom and I have always had a pretty rocky relationship, but it hasn't been bad the past few years, and I kept putting this off because I knew she would be butthurt. Sure enough, she is and thinks, "We shouldn't judge him before getting to know him and know why he did what he did" she also says it was never meant to be a secret. I'm really hurt and not sure what move to make next. I, of course, love my mom, but I don't want anything to do with her relationship, and I have kids I need to protect. What would you do???? Sorry if this is a little scattered my mind is all over the place.