The taxi driver who took the attackers to the airport came forward shortly after the attacks. His information indicated that the assailants had originally intended to detonate more improvised explosive devices. The driver, who helped lead police to a third, undetonated improvised explosive device similar to those used at Zaventem airport, told police that the attackers wanted to bring five suitcases, but only three could fit in the car.
As it happened, only two devices were detonated at the airport; the third was found and later destroyed by police. According to CBS reports, police raids have yielded two additional devices containing over 30 pounds of the improvised explosive triacetone triperoxide (TATP). These devices are probably the ones that would not fit in the cab. Had those devices been deployed and detonated, they could have caused far more damage.
Additionally, authorities have reported finding an AK-47 next to the remains of one of the airport suicide bombers. This corroborates eyewitness reports of gunshots immediately before the explosions in the airport terminal. The combination of small arms fire and explosive devices can dramatically increase the deadliness of an attack, as it did in Paris. But the assailants in Brussels were apparently unable to fully exploit that combination, which suggests that the planning for the attacks was not terribly sophisticated.
On the other hand, the group's advanced bombmaking capability is alarming. TATP is notoriously difficult to work with. It is an extremely sensitive substance, and the reaction required to synthesize it can easily cause an intense fire or an explosion. For this reason, Hamas bombmakers nicknamed TATP "the mother of Satan." Furthermore, TATP has a very short shelf life and tends to degrade quickly — sometimes spontaneously detonating as it does. Because of this, synthesizing large batches of the explosive is quite challenging.
That the Brussels cell produced dozens of pounds of TATP indicates that it includes an accomplished bombmaker. Media reports suggest that the cell's bombmaker is a man named Najim Laachraoui, who also allegedly fabricated the bombs used in the November Paris attacks. If Laachraoui was indeed the bombmaker in both attacks, he has improved his skill in the past four months.
Skilled bombmakers are a precious terrorist commodity, and finding Laachraoui — or whoever made the bombs for the Brussels attacks — before he can establish another lab and build more bombs is essential.
In their raids, Belgian authorities also found hundreds of liters of acetone and peroxide. Although we have not seen confirmation that these chemicals were industrial grade, given the large quantities we can assume that they were not consumer strength. After all, acquiring hundreds of liters of consumer strength peroxide and acetone would be onerous, as would the process required to distill them to the necessary strength. Would-be New York subway bomber Najibullah Zazi struggled with this process.
The large quantity of precursor chemicals found, plus the amount of chemicals required to synthesize the existing TATP, suggests that the cell has found a source to provide the needed chemicals in industrial quantities. Finding and stopping that source will be another important investigative initiative in this case.
The attacks in Brussels marked the largest Islamic State bombing in the West. Not only that, they are the biggest successful jihadist bombing in the West since the July 7, 2005, London bombings. This indicates that the Islamic State's efforts to improve its terrorist tradecraft and extend its reach are bearing fruit. Indeed, the Islamic State has trained and dispatched some 400 operatives to the West, AP reported on March 23. The attacks also demonstrate that clandestine cells are more capable than lone assailants. For now, though, it appears that the bombmaking skills of the Islamic State's grassroots operatives in Europe have outpaced their planning ability.