The 42-year-old, identified as Abdelaziz S, was detained on Wednesday after traces of his DNA were found on a weapon used by Coulibaly when he held shoppers inside a kosher supermarket on 9 January 2015, killing four of them.
The day before Coulibaly, working with Charlie Hebdo killers Chérif Kouachi and Saïd Kouachi, had killed police officer Clarissa Jean-Philippe.
Abdelaziz S failed to explain why his DNA was present but insisted that he knew nothing of Coulibaly's plans, police sources said on Saturday.
According to investigators, the Tokarev handguns and an assault rifle were purchased by a company owned by the wife of former mercenary and suspected arms trafficker, Claude Hermant.
Hermant claims to have sold them to another suspected arms trafficker, Samir L, as part of a police sting.
Samir L is one of several people who have been charged in connection with the attacks but, while Hermant and his wife have been questioned twice, no charges have been laid against them.