My dad who's in prison for murder sent my mom a letter instead of me...

I've made a couple posts about thus. I don't know my dad. He's been in prison since before I was born. He killed his wife who killed his kids(they were not hers). He had an affair with my mother because his wife was abusing him and his kids. People had actually said she was crazy and gonna end up killing him or his kids. She killed all 3 of them. Saddest part is there were people who heard the kids screaming but didn't want to get involved and ignored it so he had to come home to see his kids killed. He never found out he got my mom pregnant... I ended up writing him a letter explaining who I am and about me and wanting yo know him. We got a letter addressed to my mom today. She wouldn't let n read it. She teared up and just told me he needs a minute to process thus and would prefer I not write to him anymore and he will write me a letter when he's ready.... Idk what I expected... But it wasn't that...

Edit: I'm 20... I have a good relationship with my mom. I'm not !ad at her for not telling him. She said she would have but then she saw on the news what he did and what happened to his kids...