IMO he wasn't working alone. He would be alerted to anyone going in through the patio doors. He could easily then nip out through the front door. However, he knew the length of minutes between each check, so he would wait until a check was done and then enter the apartment. I think he was caught out when Gerry did his check, as Matt [I think] had listened by the apartment, he probably thought he was ok to enter after the listening by the window check, but Gerry came and he would have had to get out quickly. That is why Gerry found the door opened further than how they had left it.
So IYO he went in through the window, then was warned Gerry was coming so he had to close the window and shutters and scamper off out of the front door? Wasn't he lucky that Gerry didn't go to enter through the front door as he originally testified.
He couldn't have gone far, however, if, as some believe, Jane Tanner saw him with his black hair. If it was him, he raised the shutters, opened the window and climbed back in almost immediately after Gerry left. His accomplice must have thought that was fine, even though Gerry was still close by.
