LOS ANGELES (AP) —
    The nation's two biggest school systems — New York City and Los Angeles — received threats of a large-scale attack Tuesday with guns and bombs, and LA reacted by shutting down the entire district, while New York dismissed the warning as an amateurish hoax and held class as usual.
    The shutdown was a rare example of big city closing its entire school district because of fears of an attack. The decision also reflected lingering unease in the aftermath of the shooting that killed 14 people at an office holiday party less than two weeks ago in nearby San Bernardino.
    In LA, the threat came in the form of an email to a school board member. Authorities in New York reported receiving the same "generic" email that was sent to other cities around the country. They decided there was no danger to schoolchildren, with Mayor Bill de Blasio concluding the threat contained "nothing credible."
    "It was so outlandish," he said.
    New York Police Commissioner William Bratton agreed, quipping that it looked like the sender of the threat had watched a lot of the Showtime terrorism drama "Homeland."
    The shutdown abruptly closed more than 900 public schools and 187 charter schools attended by 640,000 students across Los Angeles.
    LA officials defended the move.
    "It is very easy in hindsight to criticize a decision based on results the decider could never have known," LA Police Chief Charlie Beck said at a news conference.
    The threatening email sent to the New York City school superintendent warned that schools would be attacked with pressure cooker bombs, nerve agents and machine guns. It claimed the writer and "138 comrades" would carry out the attack.
    Students "at every school in the New York City school district will be massacred, mercilessly. And there is nothing you can do to stop it," the message said.
    The anonymous writer claimed to be a student at a district high school who had been bullied.
    A law enforcement official with access to the document provided the email to The Associated Press. The official was not authorized to disclose details of an ongoing investigation and spoke on condition of anonymity.
    The person who wrote the note also claimed to be a jihadist but made errors that suggested the writer was really a prankster, including spelling the word "Allah" with a lowercase "a."
    The threats came in simultaneously to New York and LA school officials at about 1:20 a.m. EST Tuesday, or about 10:20 p.m. Monday in Los Angeles.
    According to LA school police, the FBI and LA police were contacted late Monday, which would mean within 90 minutes or so of the threat arriving.
    The decision to close Los Angeles schools was announced at 6:25 a.m. PST, well after NYC had already concluded the threat was a hoax and decided to keep schools open.
    Los Angeles Superintendent Ramon Cortines said every campus would be searched before schools reopened.
    Bratton called the closure in Los Angeles a "significant overreaction."
    "We cannot allow ourselves to raise levels of fear," said Bratton, who once ran the LA Police Department.
    Hours later, the ranking Democrat on the House Intelligence Committee also said the threat was believed to be a hoax.
    White House spokesman Josh Earnest said he would not second-guess the decisions made in Los Angeles or New York.
    The decision to close the district disrupted the morning routines of many Los Angeles families.
    Lupita Vela, who has a daughter in the third grade and a son who is a high school senior, called the threat "absolutely terrifying" in light of the San Bernardino attack.
    "I know the kids are anxious," she said.
    Beck said the email was specific to all the campuses in the district.
    The LA schools commonly get threats, but Cortines called this one rare and said the San Bernardino attack influenced his decision to close the entire district.
    The threat "was not to one school, two schools or three schools," he said at a news conference. "It was many schools, not specifically identified. ... That's the reason I took the action that I did."
    The superintendent said the district police chief informed him about the threat shortly after 5 a.m.
    The person who sent the threat used an "anonymizer," which uses a proxy server to mask the origin of Internet traffic, and the email was routed through a German IP address on its way to the school board member's email box, according to a law enforcement official briefed on the investigation. The official, who was not authorized to discuss an ongoing investigation, spoke on condition of anonymity.
    Vela said she worries about talking to her kids about the threat and terrorism in general. She's concerned about her daughter feeling safe in class.
    "I don't want this to be in the back of her head," she said. "Who knows what it does psychologically to kids? Is this going to cause her some kind of trauma so that she's not going to feel safe at school?"
    The closure came the same day classes were canceled at San Bernardino Valley College because of a bomb threat.