I (24F) found my husband's (26M) biological family and I wish I hadn't. Its affecting our relationship.

My husband was adopted when he was a baby. We have been together since I was 13 and he was 15. Both of his adoptive parents passed away when he was 18. It was really hard on him and he has struggled with it alot.
He has expressed in the past that he would like to find his birth family one day. He has no other family members besides his parents who passed away. His parents were VERY adament about not wanting my husband to meet or look for his birth family. We assumed it was because they did not want to feel replaced and never thought much of it. I double checked and confirmed with my husband that he still wanted to meet his birth family before I started looking for them.
We thought best case scenario they had been looking for him too and he would gain a family relationship and worst case scenario they would not want to meet my husband.
I started looking for them about 6 months ago. His birth mother had died about about a year after his birth which my husband had heard but it was hard for him to have it confirmed.
With his birth father I was sent down an absolute rabbit hole and found a TON of information. Basically his fathers birth family had killed several people. His birth grandfather and uncle were convicted for killing 2 people but they are suspected of killing up to 6. His biological Aunt was only convicted of killing 1. His birth father is suspected in several murders but they have never been able to confirm it. He was convicted for raping several children. They are all currently serving life sentences.
I told my husband what I had found and that night we watched Investigation Discovery episodes about the murders that his biological grandfather committed. The murders were absolutely horrendous, the things that nightmares are made of.
My husband is a different person since he found out. I'm not sure how to help him. Or what I can do. I know that he was really looking forward to potentially having a family, and I'm sure it's heartbreaking to know that that will never happen. I know that theres no way I could have predicted that this would have been the outcome but I feel partially responsible for not listening to his mothers warnings.
I think one of the reasons he is so upset is because he some how feels that they are a direct reflection of him.
I feel like I made a huge mistake and now I'm way in over my head here and could use some advice.
tl;dr: I found my husbands biological family who turned out to be murders. Its affecting my husband and I'm not sure how to help him.
Edit: I have asked him to go to therapy and he does not want to. I don't want to force him but does anyone have any suggestions that I could use to try to talk him into trying it? I think it would be good for him to work out issues with both his parents passing and now this information. Thanks!
Edit: Removed potentially identifying information.


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