There was a moment last summer when Belgian investigators believed they were about to nab the coordinator of the 2015 and 2016 terror attacks in Paris and Brussels.

In August, Belgian Special Forces and Brussels police conducted eight house searches across the Belgian capital. Their target: a 32-year-old Belgian-Moroccan named Oussama Atar, who investigators believe directed the deadly bombings from the Islamic State stronghold of Raqqa in Syria.

“We knew he was back,” said a senior Belgian law enforcement official. “Everyone in Molenbeek had been talking about it for over two weeks,” he added, referring to the Brussels neighborhood that was home to many of those behind the Paris and Brussels attacks. “But we missed him.”

Authorities made three arrests and took in Atar’s mother and sister for questioning, but the man they were looking for slipped their net.

Seven months later he remains at large. French and Belgian authorities say the trail has gone cold, and admit they don’t know where he is. Their best guess: Atar made his way out of Europe and is now in Iraq or Syria.

The Emir

Belgian authorities found proof of Atar's connection to the Brussels attacks on a laptop retrieved from a trashcan near a flat in the Schaerbeek district that had been a makeshift bomb factory, according to a copy of Atar’s Belgian arrest warrant filed in December 2016, and obtained by POLITICO.

Atar, also known as “Abou Ahmed,” is the cousin and alleged mentor of two of the suicide bombers who conducted the March 2016 attacks in Brussels, the El Bakraoui brothers.

Investigators extracted audio files from the computer about preparing explosives, identifying possible targets and means of attack.

“Several recordings were addressed to 'Abou Ahmed,' asking for instructions and advice,” the warrant says, specifying that the audio files were in French and the subjects appeared close, using familiar language.

The document says that at the time Abou Ahmed was in Syria and that investigators later identified him as Oussama Atar.

Belgian security and intelligence officials said they believe Atar radicalized several members of his family, including women, from Syria via encrypted channels. Officials say he was revered and often referred to as “emir,” a word indicating a leading role.

French investigators established the link between Atar and the Paris attacks of November 2015 following the arrests of two suspected extremists in Austria last December.

"They came back to Brussels because they knew it, it’s where they could get weapons, cars and protection” — Pieter van Ostaeyen, expert in Belgian jihadist networks

While in custody, one of the men, Muhammad Usman, said he intended to take part in the Paris attacks and had been sent by "Abou Ahmed." He later identified Atar as Abou Ahmed from police photos, according to a French intelligence source.

French investigators credited Atar with recruiting the two Iraqi suicide bombers who blew themselves up at the Stade de France in Paris on November 13, 2015. Following the revelations, the country’s authorities filed an international arrest warrant in December 2016.

'Gangster jihadists'

The central role Atar played in the Paris and Brussels attacks underscores the importance of family ties in Europe’s deadliest terrorist cell.

Two of his cousins blew themselves up in Brussels a year ago, killing more than 30 people: Ibrahim El Bakraoui at Zaventem airport and Khalid El Bakraoui at Maalbeek metro station.

Atar's younger brother Yassine was arrested a few days after the attack and found in possession of a key from the Schaerbeek apartment used by the attackers as a hideout and bomb factory. His third cousin, Jawad Benhattal, and his uncle, Moustapha Benhattal, were also arrested on June 17 last year.

Pieter van Ostaeyen, an expert in Belgian jihadist networks, said most of the men in the Brussels cell fall under the category he calls “gangster jihadi.”

“Criminal and family ties are interwoven,” he said. “Most of them had criminal records. And they came back to Brussels because they knew it, it’s where they could get weapons, cars and protection.”

According to senior counter terrorism officials, Atar’s “dangerous network,” includes Malika El Aroud — the widow of one of two suicide bombers who killed the anti-Taliban Afghan commander Ahmed Shah Massoud — and Bassam Ayachi, a radical imam from Molenbeek.

ISIS original

Atar first traveled to the Iraq-Syria area in 2001. He was arrested in 2005, after fighting in Fallujah as part of an Al Qaeda affiliate, according to an earlier Belgian arrest warrant against Atar, filed by Belgian authorities in March 2016 and obtained by POLITICO.

He served eight years in several jails including Abu Ghraib and Camp Bucca, where he reportedly met Abu Bakr al-Baghdadi, the current leader of Islamic State, according to media reports.

Authorities in France and Belgium have described Atar as an “ISIS original,” for his early ties to the group and previous affiliation with Al Qaeda.

He returned to Belgium in 2012 after his family campaigned for his release. Police lost track of him at the end of 2013. According to the arrest warrant, Atar’s mother told authorities in 2015 that her son had left to study at a mosque in Turkey. She described his departure as sudden — an event that surprised the whole family.

“She said she had telephone contacts with him, but denied having his contact details,” reads the warrant. The circumstances of his departure lead investigators to believe Atar might have returned to Syria before coordinating the attacks in Paris and Brussels.

Letter home

Since authorities lost track of Atar after the raids in August, the only trace of him is a letter to his mother, made public in November by Belgian daily DH.

In the letter, sent via his sister with whom he had established contact on Facebook, Atar denied having played any role in the attacks.

"No, I am not the mentor or the brain who put in place the attacks in Brussels and I was not informed about what Brahim and Khalid [the El Bakraoui brothers] planned,” he wrote.

Belgian investigators have their doubts that the letter is authentic, but the French intelligence source says it raises questions about his involvement, given that high-profile jihadists rarely distance themselves from their acts of terror.

In the letter, Atar reassured his mother that he has left Europe and has no intentions of returning anytime soon.

Given the role he allegedly played in Paris and Brussels, that gives investigators little comfort. “The cell has been weakened,” van Ostayen said. “Although I would say that some of its members are likely to still be in Europe."