its all weird, who knows, did you talk to the police, what do they think exactly?
the fact is all the idea's of it being someone you must know. theres no reason someone he knew would put the window back, likewise, some reason any burglar would put it back to stop arousing suspicion. as someone said, fairly easy to play with the window fora while appearing to be working on the house for legitimate reasons, then when the coast is clear, just pop in quickly grab something, come out, pretend to be fixing window still, leave when the coast is clear again.
but, hmm, landlord is snooping while he knows you are all away, somehow does something retarded, breaks window, piece of glass falls down, smashes screen, removes item, messes stuff up a bit, pretends it was a robbery, replaces window ¬_¬
or, i dunno where is the window in relation to everything. could someone have accidentally kicked a football through window, the went in, cleared up glass, fixed window, took screen as it was broken, left it to look like a burglary. all a bit far fetched, but it all sounds stupid anyway you think about it.