Mysterium Dortmunder U

We write the year 1973. You are criminal detectives and have been assigned the case of the mysterously disappeared CEO of the Unionsbrauerei Dortmund. While working on the case, you noticed that the janitor of said U-building of the brewery disappeared at the same time as the CEO. You sense a connection between both cases and decide to visit the janitor at his home. Upon arrival at his apartment, you notice that the doors are open. Upon entering the living room, the doors suddenly lock behind you. What happened? You find a recording device and quickly realize that you've fallen into the trap of a vengeful psychopath and that by entering the room, you've activated a bomb connected to the door, which will explode in 60 minutes. Now you ask yourselves the questions: Where is the bomb? How do we get out of here?