Go upstairs. You will see the shadow of a Splicer through a serving window, go to the window. To the right you will see a locked gate and a control box next to it. Use your Hack Tool to open it. If you are out of Hack Darts, there is one laying on a shelf in the locked room, use Telekinesis to pull it to you. After the gate is open, go through and loot the safe and the shelves. Go into the next room and drop through a hole in the floor. Now you are in a small room, and as you go to the door a gate will lock you in. Kill the Splicers to get out. Once you exit, you are free to go use the Power to the People machine, as well as gather loot and collect the Audio Diary in a side room.