Four armed robbers who shot and killed a petrol filling station attendant at Bibiani have been arrested by the police.Their names are being withheld for security reasons, the police say.The Bibiani District Police Commander, Assistant Superintendent of Police Samuel Toya, told the GNA that the four attacked the attendant, Samuel Obeng, 36, at Oando Petrol Filling Station near Bibiani Secondary/Technical School around 1830 hours and shot him, killing Obeng instantly and bolted with the money.ASP Toya said the police have impounded a Renault taxicab with registration number AS 7126 C allegedly used in the robbery.The body of Obeng has been deposited at the Bibiani Government Hospital for post-mortem.In another development, the Bibiani police have arrested 21 people suspected to be dealing in Indian hemp.Source: GNA