Two law-enforcement officials told The Daily Beast that immediately before starting his rampage, Omar Mateen called 911 and pledged his allegiance to the self-proclaimed Islamic State. (A similar pledge was made online by the San Bernardino terrorists before they shot and killed 14 people last year.) ISIS has called on Muslims around the world to attack targets in the West during the holy month of Ramadan, which began last week. The Amaq Agency, an ISIS media affiliate, later praised the attack and took credit for it. So far, there has been no established link between Mateen and the terrorist outfit.

It appears that phone call set off fears the assault on the nightclub was affiliated with the terror group, though officials said they are still not clear whether it was directed or inspired by ISIS. So far, ISIS has not claimed responsibility, but on social-media accounts associated with it, members have celebrated the shooting. It took ISIS one day to claim attack in San Bernardino.

— Nancy A. Youssef