Great guide already up, this is just for those who prefer video over text.
Once you are upstairs from the elevator, you have to sneak past 2 security guards, break the TV (By pressing A, after which the guards leave) and let Sonya in.
After letting Sonya in, she goes into the first room, DO NOT follow her. Instead keep going to the right, you see a locked door, pick your way through, and directly infront of you on the wall, is a few pictures you have to press X a couple of times.
As mentioned in the other guide, this is also a requirement for the "Sans Armes, Ni Haine, Ni Violence" Achievement