fasten itself. I took out the nail from the window on the left, but the widow still would not open. so I was there was a hidden spring somewhere, and after a while i found it. i pressed it, and then I could open the window. ' I put the nail back into its hole, and thought some more. The murderer gets out through the window, then the window drops down again behind him, and fastens itself by its hidden spring. but the nail -how could anybody put back the nail from the outside? I went to the other window and stood on the bed, looking down behind the bed head at the bottom half of the window. the nail in this window looked the same, but ..... there must be something wrong with this nail, I said to my self. I touched it - and the head of the nail came off in my fingers. The rest of the nail stayed in the wood.I carefully put the back the broken nail head,pressed the hidden spring, and lifted the window a few centimetres. the nail head went up and came down with the widow, but still looked like a real nail.? 'so,' I said, ' we know it was possible to escape through the window behind the bed head. but the room was on the fourth floor..? 'ah,' said dipin, 'that was the next question. you remember, don't you , how we walked around the building? and you saw, didn't you lightning? and the unusual shutters on the window on the fourth floor?'