i'm keiko kitagawa in tokyo. >>> schools were closed on tuesday because of a terror threat. they will remain closed until the threat is cleared. here's more. >> reporter: the unified school district is the second largest in the country. it has 640,000 students who attend 1,200 schools. and all those students stayed home because of an e-mail threat. >> the e-mail was very specific to l.a. unified school district campuses, and it included all of them. it was also very specific about the threat, the implied threat. the implied threat was explosive devices. the specific threat was attack with assault rifles and machine pistols. >> reporter: the news left parents in this area worried for the safety of their children. >> it's real. watching from what happened in san bernardino, that's pretty close to home. now this one here is even closer. that's kind of scary. >> reporter: the threat came less than two weeks after an attack by a husband and wife who were inspired by islamic state militants. the shooting in san bernard