But there are no doors between the front and back of the house. Just staircases. All it would take would be the wind coming from the right direction to create a through-draught.
No idea. But the perpetrator could have opened it. Or the neighbour could be completely wrong. The door might never have been open on that day, at that time. I'd like to see more sources for this neighbour account, personally. Sometimes people want to help, and they misremember. It might have been a different morning the door was open, or later in the day than they thought it was, more in line with the first helpers arriving once the crime was discovered. Whatever - I think LE know the truth, based on the cam footage they have acquired from neighbouring homes, and statements from the folks who actually were in the home.
MOO