After you have escorted Kruglov to Lake Yantar, go back to the downed HIND helicopter in Rostok Wildlands (where you first triggered the escort Kruglov mission). Nearby, you can see where there is an entrance to an underground garage area. Various anomalies are active in the area but are easily avoided. Looking in you can see a campfire. Go there and search around. There will be the remains of a corpse on a mattress inside a large metal ship container. Near the fire is a dead body. Search the body to find a unique handgun called Big Ben that fires PAB-9, SP-5 and SP-6 ammo. You will also acquire a new entry in your PDA (about other PDAs) with a number of notes as to what happened to Gordon Freeman.