A taxi driver stopped on suspicion of being drunk, was found carrying a police gun with its serial number filed off, Kagiso police said on Monday.
Police spokesperson Captain Solomon Sibiya said police pulled the taxi over on Dulcie September street at about 01:10 on Sunday after the driver skipped stop streets and drove recklessly.
"The police pulled the taxi aside and conducted a search, to both the vehicle and the driver who was allegedly intoxicated," said Sibiya.
A case docket of unlawful possession of a firearm and ammunition was opened at Kagiso police, and he was formally charged.
He is expected to appear in the Kagiso Magistrate's Court soon.
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The Kagiso Station Commander Brigadier Themba Maduna has decided that these stop and search operations will be stepped up on routes like Impala road next to Tshepisong, west of Johannesburg, and the R41 which cuts through Witpoortjie and Kagiso.
This followed hijackings of delivery vans, trucks and motorists by people posing as law enforcement authorities.