Thousands of internal French and Belgian documents, seen by NBC News, show a connection between an Al-Qaeda attack on Cairo in February 2009 that killed a 17-year-old French girl and wounded 24 people, and the Islamic State militant group (ISIS) network that launched the deadly attacks on the two European capitals.

A joint French and Belgian investigation focused on two of the suspects in the Cairo bombing and investigators surmised that one of the suspects, Belgian national Farouk Ben Abbes, had threatened to attack Paris’ Bataclan theater, the site of the deadliest attack in Paris on November 13, 2015, the documents show.

The same suspect had close ties to several of the attackers in Paris but, despite strong evidence, was set free and deported to Belgium from Egypt. French authorities arrested him in Toulouse after the Paris attacks but he is now free again after denying any involvement. He was an associate of Fabien Clain, whose voice claimed the Paris attacks in an ISIS audio recording.

Abbes was part of a larger European network of jihadis that would eventually lead to the deadly attacks in Paris and Brussels, but the joint Belgian-French task force failed to penetrate this cell for three years, until the task force was disbanded in 2012.

Security experts, speaking to NBC, said that this network moved from Al-Qaeda to ISIS as the latter grew in prominence to become the flag-bearer of the global jihad. The parliamentary report will examine both attacks and the failures in both cases.

The failure of Salah Abdeslam to carry out his planned suicide bombing in Paris, and the ensuing four-month manhunt and his capture, revealed a deep underground jihadi web in Belgium that centered on the Brussels district of Molenbeek. Many of the Paris attackers came from Belgium, while several lived in the suburbs of Paris.

The documents show interrogations and wiretaps carried out by both intelligence services. The associates of the Paris and Brussels attackers were under investigation but were never prosecuted, in a revelation that will shock families of the those who lost their lives in both attacks.

Catherine Vannier, the mother of the French teenager killed in Cairo, told NBC News: “If they had done their jobs properly, if they had arrested these people, I truly believe that the November 13 attack would have not taken place.”

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