On day 13 you will be dealing with cult members.
At some point in the day you will receive a call on the radio to go to the church. When you arrive you'll talk to a girl who will tell you about her father and uncle.
Go to building 621 - apartment 9 (A. Lewis). There will be no answer.
Next, go to building 609 - apartment 3 (C. F. Kane). Again, you'll get no answer, but then you will hear someone coming down the stairs.
One of the cultists will leave the building, so follow them. They will be met by other cultists along the way, and some will go into other buildings. Stick with the group until they all enter building 633.
Select the door for building 633 and select any number buzzer. When prompted make sure to select the options to keep listening/keep waiting. You will then earn this achievement.