Current and former U.S. and European counter-terrorism officials, who are experts on ISIS in Europe, told NBC News that the location and timing of the attacks — just days after the capture of the suspected operational leader of the Bataclan massacre in Paris — suggested a "shocking" level of unpreparedness by Belgian authorities.
They described Brussels, especially the Maelbeek neighborhood near the site of the subway strike, as an explosive mix of highly capable foreign fighters trained by ISIS and sympathetic locals who are unknown to authorities but eager to help in attacks.
They noted that when Bataclan terror suspect Salah Abdeslam was arrested last week, authorities found a huge cache of weapons, prompting Belgian Foreign Minister Didier Reynders to warn of other imminent attacks.
"He was ready to restart something in Brussels," Reynders said at the German Marshall Fund's Brussels Forum. Besides discovering "a lot of weapons, heavy weapons," Reynders said, "we have found a new network around him in Brussels."