The threats arrived at the same time on opposite sides of the country.
Shortly after 10 Monday night — about 1 a.m. on the East Coast — public school officials in Los Angeles and New York received nearly identical emails promising imminent attacks on campuses involving explosives and gunmen.
The immediate response in both cities was the same: Call the police and the FBI.
There, however, the parallels ended.
An hour before the sun rose in Los Angeles, the head of the sprawling school district made the dramatic decision to close the district’s more than 900 schools for the day, upending the routines for 640,000 students and setting off a massive response as police began to scour campuses.