A lockdown was lifted at Byron Nelson High School hours after officials were alerted to an alleged bomb threat Monday.
Trophy Club police said Denton County dispatch received the threatening call at 2:49 p.m.
The initial lockdown included four schools — Byron Nelson, as well as Medlin Middle School, Beck Elementary School and Lake Elementary School — and all but Byron Nelson were allowed to dismiss their students after a short time.
Meanwhile, law enforcement, including SWAT officers and the FBI, combed the Byron Nelson campus for any suspicious items.
By 6:15 p.m. the Northwest Independent School District said police determined it was safe to release the students who remained in the building.
The school district said all students were safe, and no injuries were reported.
No other details on the investigation were immediately available.
Parents who anxiously awaited for their students to be released from the lockdown said they were glued to their phones, trying to figure out what was going on.
"When something like this happens we get really scared, because that in there is our future," said parent Michael Ortiz.
Students who drove to school Monday were told to leave their vehicles in the school parking lot, and all students were also told to leave their backpacks at the school, according to the district, while police continued to investigate into the late evening.
No arrests have been made and no suspicious devices have been found, police said.
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School will be open as normal Tuesday, according to the school district, and police say extra patrols will be present.