A bit of modus operandi.
Even if an apartment looks like no-one is home, IMO a burglar may knock at the door just to make sure.
Most times when it looks like no-one is home, there really is no-one home, so the knock goes unanswered, and entry and burgalry commence IMO.
However for this the burglar needs a cover story IMO, just in case he gets surprised and someone does answer the door.
Something simple like "oh sorry I thought the so and so family was staying here".
This may possibly be what happened IMO at the apartment directly above 5G on 16 April 2007 (source: partly casefiles, partly crimewatch). There was a knock at the door, asking for someone who isn't staying there. Soon afterwards those tourists did go out, and the place was burgled.
IMO it is likely that the very first directly relevant physical event on 3 May 2007 at 5A, was that during dinner while the apartment looked and sounded like no-one was home, someone knocked at the north door and got no response.
But that is just one person''s amateur opinion and it is possible it may be wrong.
I think you are right in that some burglars do knock on doors to see if anyone is in. It happened to us. Hubby very sick in bed didn't answer the urgent knocks, but eventually struggled out to look thru the window to see burglar walking off.
Back to bed to, soon after, hear banging downstairs. Burglar had circled round in a big loop and come in via back door, which was unlocked. Was busy pulling all the saucepans out of kitchen cupboards when he heard hubby moving around. They eyeballed each other from top to bottom of stairs before burglar disappeared.
But I have to say, I am not so sure that a burglar would run if a sleepy 3-4 year old confronted him in the dark.