Help! My tenant was arrested

[Jas Singh]

I'm a first time landlady and I've already realized I few things I've done wrong in this situation. I had a tenant move in back in June through section 8. On my lease and her agreement with section 8, the tenants listed are her and her children. Her fiancé also lives with her but he's not on any of these agreements (my 1st mistake). In December there was an issue at the unit and I went to check it out and noticed the fiancé had an ankle monitor on. I was curious and decided to google but couldn't find anything (2nd mistake- I should've done a full check). I decided to look past it. A few days ago a full SWAT team was at my property, luckily no damage was done, but the fiancé was taken away in the SWAT truck. My tenant said she has no idea what happened but he does have a record. 

I had a background check done on my tenant before signing the lease and it was perfect. I'm definitely ordering a full background check on him and thinking about telling her that he can't reside in the unit. Am I allowed to do that? Any other advice on what I should do/can do? My other tenant is absolutely terrified and feel like I need to remediate the situation quickly.