radical acceptance of my thoughts is what has helped my ocd the most.
I'll give an example of what I mean:
take the stereotypical ocd compulsion of hand washing. someone in this position might have the intrusive thought "what if there's a germ on my hand that's going to get me severely ill and die if I don't wash it off in time?" now, intrusive thoughts are normal, and everyone gets these. someone without ocd is capable of moving on from this thought and letting it pass by without causing pain. but someone with ocd can't do this, they get "stuck" on the thought, which leads to obsession, and then a compulsion to try and make the pain go away (rumination is also a form of compulsion btw). so they'll get stuck on this thought "what if there's a germ" and the only way they can make the anxious thought loop stop is by giving into a compulsion "ok I'll wash my hands again, so if there was a germ it'll be gone now".
obviously the problem is that these compulsions (including ruminations) do not actually ease the source of this anxiety or prove the anxiety wrong. acting on the compulsion provides a moment of relief, and the brain interprets that as a solution. but what really ends up happening is 5 minutes later when the intrusive thought pops up again, the brain says, with even more insistence, that the only thing that can make the fear stop is if we wash our hands again. and then repeat. all day, a cycle that encourages itself, spiralling out of control, until before you know it you're washing you hands hundreds of times a day "just in case" and causing severe skin damage and bleeding and scarring. not good! giving into compulsions and ruminations feels like the solution in the moment, but they only make it worse.
the only solution is not to give in.
so when this person's thoughts say "what if there's a germ" they should, to the best of their ability, NOT give that thought any value. do not rationalize it. do not validate it. do not unpack it or examine it. and do not take preventative measures "just in case". take a step back from the thought and say "this is just a thought, I'm moving on", and then if needed say: "and if there were a germ, so what? who cares? that does not have to bother me." (after all, it doesn't bother 90% of the population. so why does it need to bother you? it doesn't.)
this is very hard to do, because your brain is screaming at you to care, but you have to stay strong and try not to care. you need to accept that the thought might be correct, and that if it were that would still be ok. you can just let there be a germ on your hands.
source for all this: years of treating my own ocd and getting to a point where I genuinely don't care if the majority of my intrusive thoughts are true or not. I get horrible thoughts about sexuality and abuse and I tell myself every time, maybe these thoughts are true, but if they were I don't care. my brain says "what if you want to do this horrible thing?" and I say "maybe I do, who cares, what does it matter either way?" and move on. all I can do moment to moment is my best, and I will continue doing my best, and obsessing over the ethics of my thoughts is not at all helpful towards my best.
does this make sense?
so, in your question I feel you asking for reassurance that this character isn't associated with that criminal. did you know obsessive reassurance-seeking is also a form of compulsion? the solution to your problem isn't to prove to yourself that the association isn't true. the solution isn't to fight that connection your brain has intrusively made – the more you fight it the worse the anxiety will be. the solution is to accept that your brain has made an association and that's ok. the association is ok. the world is not going to end because of this thought. I know it'll be difficult to accept, and you might think I'm being unreasonable with "tough love" here, but imo that's the best step forward. take a step back. agknowledge it's just a thought. and accept that it'll be ok regardless of its truth.
remember: your thoughts do not control your actions. you control your actions. your thoughts – no matter how scary they are – can not hurt you or anyone else. it doesn't matter how "bad" your thoughts are, they are materially harmless and accepting them is the only way to help them pass by like normal.
one last thing: stress makes ocd a lot worse. if it's within your ability to lessen the stress in your life, please do that.
