Terrorism is not a problem only technology can solve but one requiring strong police work:

The account emerging from French officials, witnesses and those who interacted with the suspected terrorists shows how the operation hinged on Mr. Abaaoud’s ability to use the tools of everyday modern life to lay the groundwork for the massacre. The ease with which he and his teams moved—all while avoiding detection by France’s security apparatus—suggests the challenges in identifying would-be terrorists and preventing further attacks in the fluid, digital and transnational world of today, especially when they are European citizens.

The array of car rentals, cellphones and online lodging reservations allowed Mr. Abaaoud to organize his militants as separate cells to ensure the plot wouldn’t unravel if one of the teams was compromised. Likewise, Mr. Abaaoud exploited Europe’s porous border system, sneaking stadium bombers into the continent amid the crush of Syrian refugees washing over Greece and tapping European nationals who could wield their own passports to move freely about the region.