“They are men who clearly seemed to be building toward violent acts, and whose names had surfaced in terrorism investigations, but who avoided crossing legal lines that could tip off the authorities until it was too late.” In the NYT, Rukmini Callimachi examines one of the most complex and hotly debated topics of our era: How do you stop a future terrorist when the only evidence is a thought?

+ There are tools to delete videos of beheadings and other terror-related content before it every gets seen online. Should we use them?