when Jansen joins the duo during the burglary, why does he all the way climb few floors up until he reaches the room titled "PLOUVIER" and then immediately he climbs down few steps, removes his shoes and climbs down to the theft area. By the time he removes the shoes someone watches him behind a glass window pushing the screen off, who is that?
shareWhen the Yves Montand character rings to be allowed into the building, he calls out "Plouvier" to the concierge. (The shot of the concierge parting the curtain is there to indicate that the concierge is awake/paying attention.)
He therefore walks (loudly) up all the flights of stairs to Plouvier on the fourth floor, to reinforce the sense that that's where he was going. He then takes his shoes off so that he can silently sneak back down a couple of floors to the jewelry store.