1) Do a reverse phone # lookup on the # to get the name of the person who's phone it is. Call my friend at the passport control office and tell him I'll buy him a beer after work in exchange for the passport # of that person(s).
2) When you get into the building knock on the door. If no one answers (since they are likely at work) pick the lock or just "open" the door. Grab a glass of water and walk to the balcony. If the door is answered you need to assess the situation.
a) if they do not open the door you need to get them to. When they ask 'who is it' say it Bobby Smith from the Mayors office (chances are the door will be opened.)
b) If they do not open the door fully but have a 'chain' you need to immediately rush the door to keep the chain extended then shoot the chain apart.
c) Once inside calmly level your firearm at the inhabitant(s) and explain that they are to sit down quietly and that you will be gone in 2 minutes. If they stay calm they will not be injured and they will never see you again. If they are not calm they will be shot dead on the spot. Sit them in the nearest seat you can 'attach' them to. Quickly and calmly get your glass of water, wave hello out the balcony, 'detach' the inhabitant(s) if necessary and say goodbye.
See... there is no problem that bribery or force cannot solve.
(These views are just me kidding around... but they would likely work anyway. Who says social engineering need be subtle!)