The French brothers who carried out an attack on the offices of the satirical magazine Charlie Hebdo in Paris last week received their weapons from an arms dealer in Belgium, according to Belgian media reports.
The dealer, a notorious figure from the Brussels underworld, handed himself over to Belgian police last week.
Police searched his residence and found evidence which connected him to a transaction with Amedy Coulibaly, the gunman who killed four hostages at a kosher grocery in Paris two days after Cherif and Said Kouachi killed 13 people in the French capital.
He is alleged to have sold Coulibaly the Skorpion submachine gun he used in his attack on the Jewish supermarket and the rocket-propelled grenade launcher (RPG) and Kalashnikov assault rifles that the Kouachi brothers used in their rampage through Paris.
The weapons were purchased from the dealer in downtown Brussels and cost less than 5,000 euros (£3,869).
According to Belgian media reports, the dealer is from the town of Charleroi and claimed that Coulibaly initially made contact with him in search of a car. The dealer decided to hand himself in when he realised that Coulibaly was a radical Islamist.
All three attackers were killed by French police in separate raids conducted on the Jewish grocery in eastern Paris and a printing complex in the town of Dammartin-en-Goele.