Mehdi Nemmouche, a 33-year-old Frenchman, is accused of shooting dead an Israeli couple, a local worker and a French volunteer at the museum in May 2014.
He faces life in prison if convicted of the “terrorist murder”.
Mr Nemmouche is being tried along with fellow Frenchman Nacer Bendrer, a petty criminal from Marseilles who is accused of supplying the weapons for the attack.
His lawyer, Sebastien Courtoy, referred to the juror’s colleague as “probably a person in search of attention”.
Investigators said Mr Nemmouche attacked the museum shortly after returning from Syria, where he had allegedly fought on behalf of jihadist groups.
Six days after the attack, he was arrested in the southern French port city of Marseille.
The trial is due to end in early March.
