Do you think this person knows that I'm looking at his and his friend's Facebook profile and photos?

[Pinkmelon]

First I have to admit that I fancy this guy, so I constantly check his facebook profile and some of his friends' profile and photos. Sorry if someone here hate this type of behavior, but I see nothing wrong, you like he/she, off course you will be curious and care about him/her. Now, this's my question, everytime I looked at his friends' photo albums, the next day, if I went on their profile again, the photos were all hidden (the previous day, the photo privacy was set to 'everyone' or 'friends' friend', I think), I didn't leave any comments, only browsing on my own, so I really don't know how can this happen, is this just coincident? Or is there any way to find out who check their facebook profile, who check his friends' profiles? How about if this guy knows someone working in Facebook ( though,it's very loe probability)?