my coworker has a lecherous and creepy interest in our colleague

A reader writes:

I work with a man who has an inappropriate infatuation with a much younger, married co-worker. He is married with a daughter about the same age as this woman (mid 20's). I have seen him demonstrate obsessive behavior toward her: leering, taking her picture with his cell phone, outward anger/jealousy toward anyone else who interacts with her. He pretends to be friendly to her, but makes lewd remarks behind her back about her body. He seems to have little self control and is very determined to pursue her.

At this point, I feel like talking to her and giving her a heads up that this guy's interest in her is anything but innocent. I feel like I am watching a slow-moving train wreck, and do not want to have to bear witness to this. I do believe that this is a one way obsession, and that the woman may be naive to this man's true intentions. Any insight would be appreciated.

What you described is unnerving, although it's worth noting that we don't actually know whether the woman might in fact return his interest, married or not. Either way, though, the lewd remarks behind her back and the aggression toward others who interact with her are alarming -- and those are also the two elements that indicate to me that you should say something. Otherwise we might just have a douchey guy with an inappropriate crush, but those elements elevate it to objectively creepy.

(By the way, I can't tell if the cell phone pictures are being taken with her knowledge/cooperation; obviously, if they're not, that's highly creepy element #3. Beyond creepy, in fact.)

I think the right thing to do in this situation is to mention to her what you've seen, but stick to the facts. Rather than telling her that he's determined to pursue her and has little self-control -- which I don't think you can actually know -- tell her what you do know for sure: He makes inappropriate remarks about her when she's not around and sometimes becomes hostile when others talk to her. And if she doesn't know about the photo-taking, you absolutely must mention that too, as it's a huge violation. 

From there, it's up to her to decide how she wants to handle this. If she seems freaked out but uncertain what her options are, suggest that she speak to her manager and/or HR. Or, it's possible that she won't care or will choose not to discuss her reaction with you, in which case this probably needs to become none of your business, unless you see it escalate to new worrrisome behaviors (in which case you should fill her in again).

However, there's one piece that will remain your business regardless of how this plays out, and that's what the guy says in front of you. If he's making inappropriate remarks about her (or anyone), speak up! Tell him it's inappropriate for the office, disrespectful toward her, and something you don't want to hear again.

I'll also add this: If your gut is sending you warning signs that this guy isn't just a lech but is also potentially dangerous in some way, read The Gift of Fear and encourage your colleague to also. It gives really helpful advice on knowing when someone is just kind of a jerk or socially inept versus when you should be more worried. (Actually, everyone should read this.)

What do others think?