Los Angeles Police Chief Charlie Beck defended the decision to shut down the L.A. school system on Tuesday over a sensational terror threat that was later deemed a hoax.

L.A. officials cancelled classes in the nation's second-largest school district after receiving an email late Monday night from someone threatening to attack multiple schools in the city with explosives and gunmen, reports The Los Angeles Times.

The person who wrote the email appeared to be a devout Muslim who planned to launch an attack using bombs, nerve gas and rifles on Tuesday, said Democratic Rep. Brad Sherman of California, according to the New York Times. Sherman said the email listed every school in the Los Angeles Unified School District and warned that explosives had already been planted. After they detonated, people "with ISIS connections" would attack with AK-47 rifles and other guns, said Beck paraphrasing the email.

The head of the L.A. school district then made the dramatic decision early Tuesday morning to close the district's more than 900 schools for the day.

A similar emailed threat was also sent to New York City's public schools at the same time Monday night. However, New York officials dismissed it as a hoax and kept schools open. New York City Police Commissioner William Bratton and federal officials also criticized authorities in Los Angeles for overreacting to the email.

The move in Los Angeles was "a significant overreaction," said Bratton, who once ran the LAPD. "We cannot allow ourselves to raise levels of fear. This is not a credible threat and not one that requires any action."

He added that another clear sign of the email being a hoax was the fact that it was written "in very good English -- which is not a good sign," he said.

NYC Mayor Bill de Blasio described the email threat as "generic" and "outlandish," adding that it was hard to take the threat seriously.

In response, Beck fired back, saying, "It is very easy in hindsight to criticize the decision based on results that the decider could never have known," reports Reuters.

"It's very easy to second-guess decision-makers when you don't have to live with the consequences of the decision. These decisions are not something you get to do over again if you turn out to be wrong," he said.

Later in the day, he conceded that the threat was not credible.

Officials also conducted an extensive search of the schools in the Los Angeles Unified School District before announcing that schools were set to reopen on Wednesday. Beck added that police officers would be deployed at city schools to quell any remaining fears.