I just think if he had used that house before he would have found an easier way in and out.
I thought the same thing, but perhaps he DID have easy access. I read the last time the owner of the house visited was in November. Perhaps before then Harley had access through a unlocked window or somehow knew the code on the lockbox.
Then when the owner visited in November he either locked the windows, made them more secure or change the code on the lock box?