In the basement you will find the members of Samizdat in the cells along with a number of other augmented people. You need to figure out the way to open these cells. There is a Keypad (Security Rating 1) found in the Northwestern part of this room. Much like any police station you have visited you will find a lot of ammo and other useful items scattered around a side of the area. Pick up it to bolster your stocks.
Having collected what supplies you can, head over to the Eastern cell to open it up. This will trigger a cutscene and begin the next part of the mission. After you talk with with the former K about what has happened, you will have a number of options on how to get them through to the escape site. Unless you have cleared the streets prior to getting inside the police station, choose either "play it cool" or "wait here". Choosing "Play it cool" will get them to impersonate cops, which makes it very easy for them to slip through the area without detection.