French police said on Saturday they had detained a person believed to be a former roommate of the man who attacked two people in Paris near the former offices of the satirical magazine Charlie Hebdo.
Late Friday police released a 33-year-old Algerian man who was a witness and had "chased the assailant," after the investigators corroborated the man’s account.
As of Saturday morning, a total of seven people remained in custody in connection with the Friday’s attack, including the suspected perpetrator.
The attacker was identified as an 18-year-old Pakistani man, who arrived in France three years ago as an unaccompanied minor.
French authorities launched an anti-terrorism investigation after the attack on Friday.
In an interview with France 2 television station, French Interior Minister Gerald Darmanin said the attack was "clearly an act of Islamist terrorism."
"Manifestly, the method was one of an Islamist terrorist. There is little doubt this is a new bloody attack against our country, against journalists, against our society, which you already mentioned in your report... a great amount of difficulties and emotions over the past few years and I would like the extend my support to them as well," Darmanin said.
France's counterterrorism prosecutor, Jean-Francois Ricard, said the young man was arrested with another person not far from where the attack took place.
Ricard said the attacker did not know the victims - a woman and a man from a documentary production company on a smoke break.
The motivation for the attack and whether it had any connection to Charlie Hebdo is unclear.
Islamist militants attacked the Charlie Hebdo offices in 2015, killing 12 people.
A terrorism trial for 14 people accused of being accomplices in that attack is currently going on in Paris.
Charlie Hebdo angered many Muslims by publishing cartoons featuring the Prophet Muhammad, and ahead of the trial it recently reprinted some of the same cartoons.
Last week, police moved the magazine’s head of human resources from her home after she was the target of death threats around the start of the trial.