The GSU officer based at the Ruiru General Service Unit stole on Saturday a Jericho pistol and tried selling it at Sh100,000 to a broker in Kawangware.
The pistol was taken out of the armory with 15 bullets.
The said officer was arrested by the Flying Squad, Presidential Escort and DCI Dagoretti police unit officers, and the gun traced to a Kawangware gangster.
He is expected in court on Monday.
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