The Fearsome Dr. Crane - S1-E14
Continuity mistake: When Nygma examines the corpse, he pushes his right hand deep into the body. When he is caught, he holds both hands up in the air. The glove on his right hand is completely clean, when it should be covered in blood and gore.
Answer: "The Merc" was a warehouse like store with aisles that sold mainly weapons, machetes, AK-47s, C-4, barrels of acid, etc. In s02e05, "Scarification", it was shown being raided by GCPD.
Bishop73