According to VChK-OGPU and Rucriminal.info, the explosion at the commandant's office in Sertolovo, Leningrad Oblast, occurred on the floor occupied by officers of the FSB's Military Counterintelligence Department.
The epicenter of the explosion was on the third floor of the building, which six months ago had been converted into a military counterintelligence department and occupied by officers of that unit.
The second floor houses the Military Field Bank.
The explosion killed three people, and several were injured.
Our source immediately recalled a story about how officers from the FSB's Military Counterintelligence Department brought a drone they had discovered into the building, which then exploded.
