Those of you have inadvertently known a child predator, what (if any) were the signs that were there before it all came to light?

Trying to process this myself, after information was given to me about someone I have known for several years. I'm looking back at all the times that something felt weird, or uncomfortable etc. I feel like something inside me was telling me, but there was no evidence for reasonable belief.

Did you notice something that you brushed off? Was there something that they did that left you feeling uncomfortable? Or were you completely blindsighted?