The source said Anis would be charged on Friday.

According to Italian anti-terrorism chief Lamberto Giannini, French investigators are looking into whether Anis “indoctrinated… Ahmed and caused his radicalisation”.

He was arrested in the northern Italian town of Ferrara six days after Ahmed Hanachi, a 29-year-old Tunisian, fatally stabbed the two women outside Marseille's main rail station on October 1 before being shot dead by police.

Extradition from Germany

Shortly after on Friday, the AFP news agency reported that a Moroccan man suspected of helping to plan a 2015 attack on a Paris-bound train had also been extradited to France, this time from Germany.

Redouane Sebbar, 25, was a close associate of Abdelhamid Abaaoud, the ringleader of the 2015 jihadist attacks in Paris that claimed 130 lives.

Abaaoud, who died in a police raid days after the carnage in the French capital, is also believed to have ordered the attack on the high-speed Thalys train from Amsterdam to Paris on August 21, 2015.

The pair made several European trips together.

The legal source said Sebbar, who had been in custody in Germany since late 2016, was extradited to France on October 26 and charged with “complicity in attempted terrorist murder”.

His fellow Moroccan Ayoub El Khazzani, a member of the Islamic State group returning from Syria, opened fire with a Kalashnikov on the Thalys train just after it entered France, wounding two people.

Three Americans holidaying in Europe — two of them off-duty servicemen — overpowered him, saving passengers from what could have been a bloodbath.

Khazzani told investigators he was acting on the orders of Abaaoud, whom he met in Syria.

French investigators became interested in Sebbar after noticing he made a return Thalys trip from Brussels to Paris a few days before Khazzani's attack.