Prime suspects: Cheir and Said Kouachi
Prime suspects: Cheir and Said KouachiFrench police

The two prime suspects in Wednesday's deadly attack on French magazine Charlie Hebdo's Paris offices have been spotted by witnesses in northern France - where they apparently robbed a service station.

The service station's manager said Cherif and Said Kouachi entered into the service station near Villers-Cotterets in the Aisne region at 10:30 a.m. local time, and were armed with Kalashnikov assault rifles - the same weapons used in yesterday's attack - as well as rocket-propelled grenades.

It follows further dramatic developments on Thursday, when a policewoman was shot dead and another person injured by an unidentified gunman in Paris. It is not yet know whether that attack is related to the investigation into the Charlie Hebdo attack.

The armed suspects made their getaway from the scene of the robbery in a Renault Clio - the same make of car reportedly stolen by them after the Paris attack. Witnesses said they drove off in the direction of Paris. 

Police already have their third prime suspect, named as 18-year-old Hamyd Mourad, in their custody, after he voluntarily handed himself over last night.

Seven others have been arrested as part of the ongoing police operation to track down the terrorist killers.

Questions are already being asked as to how Cherif Kouachi , who was jailed for three years in 2008 for helping recruit French Muslims to fight for Al Qaeda in Iraq, could have been able to plan and carry such a brazen attack in broad daylight under the noses of intelligence services.