It is not yet clear what caused the collapse, but local media reports said severe cracks were detected in the block on Tuesday.

BBC: Bangladesh Dhaka building collapse leaves 87 dead

Once the department had Tamerlan under surveillance, the NYPD's cyberunit might have detected his suspicious online viewing choices and social-media postings.

WSJ: Judith Miller: How to Stop Terrorists Before They Kill

The social media giant said in a blog posting that earlier this week it detected attempts to gain access to its user data.

NPR: Twitter Says Hackers Compromise 250K Accounts