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One week after the horrific school massacre in Connecticut, nearby campuses and many across the country Friday were flooded with threats of violence that sent police swarming onto school campuses, disrupted classes and worried anxious parents.
Authorities investigated threats at four local high schools and at numerous schools in 11 other states. None were found to be credible.
Diamond Ranch High School in Pomona was placed on lockdown for nearly four hours, as 20-30 sheriff deputies searched the school in an effort to root out a threat made by an anonymous caller against the school and the student body, authorities said.
High schools in South Pasadena and La Mirada received extra police and sheriff's patrols in response to unsubstantiated threats.
And in Chino Hills Thursday, a student was arrested on suspicion of causing a disturbance on school grounds after he allegedly donned an Albert Einstein mask and ran around scaring fellow students.
"People are reacting to what happened in Connecticut and taking advantage of that to disrupt the learning environment," Norwalk-La Mirada Unified School District Superintendent Ruth Perez said.
Others suggested the pranks and threats were in response to the news of the turning over of the Mayan calendar, which some fringe groups interpreted as the the end of the world come Friday.
"This is the day the Mayan calendar says the world is going to end," South Pasadena Unified School District Superintendent Joel Shapiro said.
"If you're looking for pranks, this is the day we're likely to get them."
Hundreds of parents waited outside Diamond Ranch, located at 100 Diamond Ranch Road, during the morning and afternoon to pick up their children. The lockdown was called off around 12:45 p.m. The threat, received by administrators around 9 a.m., was not substantiated, Los Angeles County sheriff's Sgt. Al Fulkerson said.
The school was notified of the threat by the Sheriff's Department shortly before 9 a.m., said Pomona Valley Unified School District Superintendent Richard Martinez. The school had a late start schedule Friday - the last day of classes prior to winter break - for final exams.
Martinez said administrators received a "very general" threat against the school.
"The students are safe," he said, adding that the campus lockdown was a "precautionary measure."
Students who had already made it to campus by about 9:05 were kept inside classrooms, which were in constant communication with the school office, Martinez said.
Students who showed up later were turned around and told to head home for the time being.
It was not known how many of Diamond Ranch High School's 1,950 students were on campus during the lockdown as deputies went room to room before giving the all clear.
"This is protocol," said Sheriff's spokeswoman Nicole Nishida. "Once it goes into lockdown, we want to make sure everyone's safe in every classroom.
Xavier Navarro, 38, of Pomona, waited outside the campus Friday to pick up his son, an 11th-grader. "Once I get him, I'm just going to hug him and take him home," the father said.
He said the situation appeared to be under control, though he was very worried during the first hour of the lockdown, when he said he and other parents had no information about what was taking place.
"I've never been this scared in my life," Navarro said.
In the wake of the recent tragic shooting in Newtown Conn., Navarro said school security should be a top priority, "even if it means an armed guard at every school."
Arrangements were being made to re-schedule final exams when school reopens in January, officials said.
At South Pasadena high, police investigated a threat of gun violence after receiving a tip from a student late Thursday, officials said.
A female student told police that a person described only as a male wearing a hooded sweatshirt told her during the school day Thursday something to the effect of, "Don't come to school tomorrow. There's going to be a shooting," South Pasadena police Detective Richard Lee said.
Police did not learn of the alleged threat until about 9 p.m. Thursday, officials said.
The student initially posted about the threat on Facebook, Shapiro said. "Fortunately, her father saw it and reported it to the police," he said.
The source of the potential threat remained unclear Friday, Lee said.
There were also some inconsistencies in the accounts the girl told investigators, he said. "That inconsistency leads (police) to call it a non-credible rumor."
Nonetheless, extra officers were sent to patrol the campus Friday, the last day of school at the campus before winter break, officials said. The school was not planning final exams until after the winter break.
Other schools in the district were also receiving extra police patrols, he added.
La Mirada High School had enhanced security on campus Friday after hearing about rumored threats that a shooting was going to take place at the school Friday.
Norwalk deputies visited the school earlier this week and interviewed students and the school's principal Bill Seals.
"We discovered (the threats) were unsubstantiated rumors that were brought to the school's attention about a possible shooting that may take place Friday," Sgt. James Franck said.
On Thursday, the last day before winter break, Ayala High School in Chino Hills had a brief security lock down.
"There was a student running around, scaring students," Chino Valley Unified spokeswoman Julie Gobin said Friday.
Student Kritesh Bhakta was allegedly racing around campus, wearing an Albert Einstein mask, according to San Bernardino County Sheriff's Department spokeswoman Cindy Bachman.
Seeing the mask-wearing student, Ayala High students ran into the front office in a panic, and officials triggered the lock down, which lasted about 10 minutes.
"They didn't recognize the student and he was pulling a prank," Gobin said.
Bhakta reportedly ran off campus and was later arrested by a campus security guard and a San Bernardino County sheriff deputy. He was booked at West Valley Detention Center for causing a disturbance on school grounds and released Thursday night with a citation.
Police had investigated a rumor of a possible threat against the school earlier in the week.
Similar scares played out Friday throughout the nation as threats of violence and rumors of threats hit schools in states including Michigan, Idaho, Pennsylvania, Maine, Illinois, California, Florida, Utah, Texas, Oregon, Washington, and Oklahoma.
A number of schools were also closed in New Milford, Conn., about 10 miles from Sandy Hook Elementary School in Newtown. Other schools were inundated by threats in Michigan.
"The process of education has just been so disruptive that it was a unanimous decision by all superintendents" in Lapeer County to shut down, Tom English, superintendent of North Branch Area schools told the Detroit Free Press. "We're not happy about it."
One student, a 16-year-old in Oakland County, Mich., was arrested for threatening to come into school on Friday and "shoot people," The Oakland Press reports.
The story was similar in Oklahoma, where schools in Caney Valley were closed.
"They installed a doorbell, they locked all entrances into the school, and the only way after the bell had rang in the morning that you could get in was by ringing the bell and an employee letting you in," substitute teacher and mother Kami Asbury told Tulsa's Channel 8.
A school district near Boise, Idaho, canceled planned assemblies at a number of its 50 schools after receiving a rash of threats that suggested "something bad" would happen on Friday, Meridian school spokesman Eric Exline said.
In Florida, a 13-year-old student was arrested on Thursday after he allegedly posted a Facebook message threatening to "bring a gun to school tomorrow and shoot everyone," said the St. Lucie County Sheriff's office on Florida's east coast.
An administrator in Idaho seemed best to sum up the mood in school districts across the country.
"The reason we're canceling school is not because we think there is a credible threat but because the fear and the panic is just so palpable that we didn't believe we could have a productive, calm day," Coeur d'Alene Superintendent Hazel Bauman told the Spokesman-Review.
Doug Saunders, Digital First Media staff and Reuters contributed to this report.