Hunting for controllers

After killing all controllers at Radar and shedding some light onto the story of their appearance, you come to Yantar to kill the rest.
== Walkthrough ==
There are 5 controllers total.
On one of them, you can find a voice recording device. By examining it, you can discover that the head of the lab performed a test of an unknown substance on his unsuspecting subordinates, disguising it as a "vaccine", and they turned into controllers as a result.
After killing all of them, Crazy doctor is triggered.
== Notes ==
* Just like the previous one, this quest assumes you already know the transition from Radar to Yantar, obtained for Attache case from the security checkpoint. It's not a requirement, but will make the quest seem more logical.
== Bugs ==
* Some controllers can disappear under the level geometry and appear later.