The New York Times reports: Investigators found crates’ worth of disposable cellphones, meticulously scoured of email data. All around Paris, they found traces of improved bomb-making materials. And they began piecing together a multilayered terrorist attack that evaded detection until much too late.

In the immediate aftermath of the Paris terror attacks on Nov. 13, French investigators came face to face with the reality that they had missed earlier signs that the Islamic State was building the machinery to mount sustained terrorist strikes in Europe.

Now, the arrest in Belgium on Friday of Salah Abdeslam, who officials say was the logistics chief for the Paris attacks, offers a crucial opportunity to address the many unanswered questions surrounding how they were planned. Mr. Abdeslam, who was transferred to the penitentiary complex in Bruges on Saturday, is believed to be the only direct participant in the attacks who is still alive.

Much of what the authorities already know is in a 55-page report compiled in the weeks after the attack by the French antiterrorism police, presented privately to France’s Interior Ministry; a copy was recently obtained by The New York Times. While much about the Paris attacks has been learned from witnesses and others, the report has offered new perspectives about the plot that had not yet been publicized. [Continue reading…]