All of Europe was looking for Abdelhamid Abaaoud, the planner of the Paris attacks. One woman helped him plan the carnage; another woman turned him in.
Belgian prosecutors launched a public appeal Thursday seeking any information on "the man in a hat" seen before the Brussels Airport suicide bombings.
Brussels victims included commuters heading to work, travelers starting long-anticipated vacations, expatriates setting out to visit distant homelands.
The bomb maker, the transporter, the landlord and the cipher. The four men slipped away after the Nov. 13 attacks in Paris, and all but one helped in Brussels.
John Kerry is holding counterterrorism talks in Brussels on Friday as top members of Belgium's embattled government face ongoing criticism.
9/11 and Brussels similarities: Intelligence leads that could have led to the terrorists were misplaced or overlooked.