Detectives based in Ruiru on Monday evening impounded Ksh350m in fake US dollars and pounds within BTL area in Ruiru.
The team also recovered one Glock pistol and 28 rounds of 9mm ammunition during the raid which saw three Cameroonians arrested.
Two of the suspects, Paulin Francis Proper and Njikam Omar, were discovered to be in the country illegally. The third suspect Job Kentong was found holding a refugee identity card.
During the raid, detectives also discovered 250 kilograms of fake gold nuggets and gold bars.
Further interrogation on the main suspect Paulin Francis led detectives to his home in Muthaiga North where the firearm was discovered.
Detectives also arrested the fourth suspect Loise Kaguong who is believed to be the owner of the gun that was recovered in Muthaiga North. The gun license had expired.
Loise is suspected to be the leader of the syndicate that is defrauding Kenyans of their hard-earned cash. She is said to be operating over 10 mobile money outlets.
The arrest comes a day after detectives based in Mombasa arrested two suspects after they were found with fake bundles of notes.
The two, Jamil Salman Abdul, 43 and 30-year-old Tesfawork Ermias Dogso were also found operating in the country illegally.
Detectives intercepted a Nissan Note, KDA 505Y, that the two had boarded, and discovered a khaki envelope bearing 198 forged Euro notes in 100 denominations hidden between the driver and co-driver seats.
According to detectives, all notes recovered in the raid bore similar serial numbers – BCE ECB EZB EKT EKP 2002 – and more