A bomb maker, a safe house, and a suicide note: What we know so far about how the Paris and Brussels attacks are linked

Links between Tuesday's attack in Brussels and the November Paris attacks are piling up as details emerge about the suspected Brussels bombers.

The links appear to pivot around two men in particular - Najim Laachraoui and Salah Abdeslam - and the Brussels apartments they used to hide from police and build bombs.

Najim Laachraoui, 24, was apparently a bombmaker for ISIS before he detonated himself at Brussels airport along with 30-year-old Ibrahim El Bakraoui on Tuesday.

Only one day before the Brussels attacks, Laachraoui had been named by Belgian officials as a suspected accomplice of Salah Abdeslam - the sole surviving suspect in the November Paris attacks that killed 130 people. Laachraoui is believed to have traveled to Austria from Hungary with Abdeslam in September 2015.

Abdeslam was detained in a raid on March 18th and charged in relation to the Paris attacks, and his lawyer insisted that "he was not aware" that the attacks on Brussels airport and a metro station in the government district were being planned.

But Abdeslam's fingerprints were found at one of the apartments authorities believe was rented by Khalid El Bakraoui - Ibrahim El Bakraoui's brother, who killed 20 people when he detonated himself at Maelbeek metro station - in the Forest district of Brussels. Indeed, Abdeslam now appears so enmeshed with the Brussels attackers that investigators believe he would have been involved in the plot had he not been captured days prior.

Significantly, Khalid El Bakraoui was sought by Belgian prosecutors for his alleged role in the Paris attacks months before the Brussels terror plot was carried out. Authorities reportedly issued a warrant for Khalid's arrest in December, and suspected that he had used a false name to rent a Brussels apartment in Charleroi and use it as a safe house for the Paris attackers.

Laachraoui's DNA, meanwhile, was found on suicide vests used by the Paris attackers and in the Brussels apartment where they were made, a French police source told the Associated Press. He is believed to have made all of the suicide vests worn by the Paris attackers.

Will McCants, author of "The ISIS Apocalypse," noted that the extent of the suicide bombers' connection to the Paris attacks - and to ISIS more broadly - rests largely on Laachraoui's involvement, as the bombmaker "would have been their handler," McCants told Business Insider on Wednesday.

A suicide note thought to be written by Ibrahim El Bakraoui offers further clues of a link between Abdeslam - Laachraoui's alleged accomplice in the Paris attacks - and the Brussels attacks. El Bakraoui apparently wrote in French that he was in "a bad situation" and that, if he did not act immediately, he would end up in a prison cell "like him."

"The note would confirm the speculation that the attackers moved up the timetable because Abdeslam was arrested," McCants said.