How Ukrainian intelligence chiefs are tracking down collaborators who worked with the Russians

When Russians took over the city of Balakliya, eastern Ukraine, they turned the central police station into a base for brutality.

During the six months it spent under enemy occupation, scores of local residents were locked in overcrowded cells in the basement. Survivors told of being dragged to a torture chamber where they were beaten, electrocuted and forced to endure mock executions.

The interrogations were carried out by officials from Russia’s Federal Security Service, according to documents retrieved after the town’s recapture last month during Ukraine’s stunning counter-offensive.

Yet the interrogators were helped by local stooges – such as Oleg Kalaida, the jobless former head of security at a chicken farm who found himself elevated to chief of police after agreeing to serve as a Kremlin henchman.

The horror stories emerging in liberated towns such as Balakliya, a railway hub of 30,000 people, have become hideously familiar in recent months: of Russian atrocities, mass…