In Los Angeles County, 1,531 school sites had been walked through and inspected over the course of the 12-hour investigation, officials said.
Extra police patrols will be assigned to all schools to ease students back into normalcy, LAPD Chief Charlie Beck said.
All schools in the Los Angeles Unified School District were shut down today following an emailed threat mentioning violence against students, including attacks assault rifles and an implication of explosive devices, police said.
NYPD Commissioner Bill Bratton, who once ran the LAPD, today criticized the response of the LAUSD, saying officials there overreacted.
"This is not a credible threat. This is not something that we’re concerned with," said Bratton. "What we would be concerned with is overreacting to it. We’ll stay aware, we’ll stay involved. But at all costs cannot start overreacting to what will possibly be a series of copycat initiatives."
"I think - the initiator, the instigator of the threat may be a 'Homeland' fan," Bratton added. "It mirrors a lot of recent episodes on 'Homeland.'"
But LAPD Chief Beck fired back at the assertion.
“The school district safeguards three-quarters of a million lives every day,” Beck said. “I think it’s irresponsible, based on facts that have yet to be determined, to criticize that decision [to close the schools] at this point."
Two law enforcement sources said the letters to New York City and LA “may very well be identical” in terms of content and origin.
The Los Angeles closings were made out of “an abundance of caution," the LAPD said. A California law enforcement official told ABC News the threat was not serious and the LAPD was not on tactical alert. The threat is not connected to any previous threats or the San Bernardino terror investigation, a senior law enforcement official said.
The threat received in Los Angeles this morning was emailed from outside the country, according to two law enforcement officials briefed on the investigation. The last IP address li
nked to the email threat came from Frankfurt, Germany, according to an LAUSD official.
According to Garcetti, the email threatened violence to students.
“The email was very specific to L.A. Unified school district campuses and it included all of them,” Beck said. “The implied threat was explosive devices. The specific threat was attack with assault rifles and machine pistols."
LAUSD Superintendent Ramon Cortines said today the threat mentioned backpacks and "other packages."
“These obviously are things that we take very seriously,” Beck added. “We worked with the FBI to vet this as best as possible.”
A police source told ABC News the threat to New York City schools was received via email around 5 a.m. and was similar in nature to the threat made to Los Angeles schools.
Rep. Adam Schiff, D-California, the ranking Democrat on the House Intelligence Committee, said “the preliminary assessment" of the threat is "that it was a hoax or something designed to disrupt school districts in large cities.”
De Blasio called the threat “outlandish" and generic, saying it would have been a "huge disservice” to close the schools.
Garcetti said the decision to close schools was not his to make -- unlike New York where schools are under mayoral control -- but he supported it.
“Usually what people think in the first few hours is not necessarily how it plays out in later hours. We see investigations unfold sometimes for a series of days,” he said. “But decisions need to be made in a matter of minutes.”