ROME — When Tunisian native Ben Mehedi Nasr was arrested in the town of Novellara in 2007, he was considered one of the most dangerous terrorists in Italy. When he was picked up in the north-central Reggio Emilia province, authorities had been tracking him and 16 Tunisian associates who they referred to as the “17 fratelli” who had settled legally in the country. It was long before an exodus of migrants and refugees started coming, back when it was common for those wanting to settle in Europe did so by commercial ferry, as Nasr had done.

But soon after his arrival, authorities suspected Nasr, then 31, was up to no good. He had a legitimate job as a construction worker by day, but there were also reports that he was helping radicalize young Muslim men at evening gatherings in the local Islamic Center and at a 24-hour phone facility that offered special rates for calls to the Middle East. It was then that anti-terrorism police started bugging his phone and those at the call center.

During that time, authorities collected valuable intelligence that was shared with the U.S. and the U.K. about a terrorist cell that recruited young men to fight for al Qaeda in Syria, Iraq, and Afghanistan. Nasr was thought to be one of the leaders, along with Dridi Sabri, who had set up a similar structure in Milan, and Imed Ben Zarkaouwi, who traveled between Reggio Emilia and Milan. All four were arrested in November 2007 in joint sting operations.

According to testimony presented at his trial, Mehedi Nasr was an explosives expert whose recruitment skills for would-be jihadi fighters was second to none. Among the things they found in his apartment were colorfully illustrated bomb-making manuals in Italian, French, and English, and a lively hip-hop video that apparently showed the perks of suicide bombing. Authorities also described a “suicide-bomber factory” in a Milan apartment block, where young men were trained under harsh psychological circumstances before being sent to fight. Police also identified an arms-trafficking network through which illegal weapons were being smuggled via traditional organized-crime routes. Those activities were curtailed with the arrest and convictions of 15 of the 17 Fratelli group, including arms runners who had set up links in France, Portugal, and the U.K.

All of this was presented in a 500-page dossier that sealed Nasr’s conviction on terrorism charges in early 2008, for which Judge Luisa Savoia sentenced him and his associates to eight years in prison. He admitted knowing the other men, but claimed he was innocent. “I’m not part of any organization,” he told the court, according to transcripts. “I met the head of the cell in Milan [Sabri] twice, but then I’ve had no contact with him for two years.”

He was sent to a maximum-security facility in Naples to serve his time. In late 2008, anti-terrorism prosecutor Andrea Santucci offered him a deal for early release in exchange for testimony against the others in the Italian cell, but he refused, according to Vainer Burani, his lawyer at the time. (Burani told The Daily Beast he has not heard form his former client since his release.) A few months after the offer, his cousin Mourad Nasr, was arrested on charges that he took over as head of the cell. He was released from prison in 2014 and immediately repatriated to Tunisia.

On Oct. 4 of this year, Nasr came back to Italy. This time, he tried to sneak in as part of a group of 200 Syrian refugees who set sail from Libya and were rescued by the Italian navy during one of the many Mediterranean rescue operations. He was taken to Lampedusa, where Sicilian authorities immediately separated him and three others from the rest of the group in what has become the usual practice of racial-profiling. He was obviously not Syrian, so they immediately thought he was one of the traffickers.

Instead, he claimed that his name was Mohamed Ben Sar and even had a Syrian document that he said proved it. He said he wanted to claim political asylum in northern Europe, but officials didn’t believe him and ran his fingerprints through Italy’s extensive AFIS digital database, where he was identified immediately as Ben Mehedi Nasr, one of the most dangerous terrorists known to Italian authorities.

Yet rather than questioning his motives for returning, authorities confirm Nasr was sent back to Tunisia on Monday under a bilateral agreement that requires automated repatriation for any Tunisian citizens illegally entering Italy who are not suspected of being traffickers. On the boat that Nasr came over on, authorities identified other men who they charged with navigating the vessel—which means Nasr isn’t suspected of any crime, despite his criminal history. “It’s a big of a loophole. He wasn’t suspected of recruiting anyone or doing anything but entering the country illegally,” a spokesman for the police in Agrigento, who saw to his repatriation, told The Daily Beast. “We may never know his real intentions.”

Indeed, hopefully we never will.