Anis Hanachi, 25, was arrested in the northern Italian city of Ferrara, where he had been living with a fellow Tunisian, on Saturday after French authorities issued an international arrest warrant. He is accused of being complicit in his brother's attack and of participating in a terrorist organization.
His brother Ahmed killed two cousins, both aged 20, on October 1st at Marseille's Saint-Charles train station before being shot dead by anti-terror troops.
Ahmed had spent several years in Aprilia, a town south of Rome, where he married, and later divorced, an Italian woman in 2008 and was registered as a resident between March 2010 and 2017.
French authorities told their Italian counterparts that Anis had been a jihadist in Syria between 2014 and 2016 and is believed to have radicalized his brother.
The investigation since his arrest also revealed that he had been sent back to Tunisia from Italy after arriving on the southern island of Favignana in 2014 on a migrant boat.
Police said at a press conference on Monday that “there is no evidence” so far to suggest that Anis was planning terrorist attacks in Italy or that he had “solid support” for logistics in Ferrara.