Assistant Police Chief Kevin Colby said detectives have begun interviewing 18-year-old Timothy George Simpkins, who will be charged with three counts of assault with a deadly weapon.
Four people were injured in the shooting at Timberview High School. Two of the four were shot and three were hospitalised.
All three admitted to the hospital are expected to survive, Colby said. He said a male student who is in the intensive care unit has no longer had surgery.
An adult male hospitalized is in good condition, Colby said. Arlington Police spokesman Tim Sisko said a teenage girl who may have been crushed by a bullet was released Wednesday night and is in good condition with abrasions.
Officials said around 1,700 students were in the school and all have left the building.
Mayor Jim Ross said the first reports of shootings on the second floor of the school came at around 9:15 a.m. (10:15 a.m. ET).
Police said the bullet may have happened after a fight between a student and another person during class.
Officers launched a “duly search” and worked with several local police departments and the Bureau of Alcohol, Tobacco, Firearms and Explosives, Arlington Police tweeted.
The department tweeted a photo of Simpkins asking for the public’s help in locating him.
By noon, Simpkins was in custody.
Arlington Police said a weapon was recovered in “the streets of Grand Prairie” a few miles from the high school.
Grand Prairie Police said the weapon recovered was a .45-caliber handgun.
Chief Daniel Cessani said police believed it was a weapon used in the school shooting, but this has not been confirmed. He said the gun has been handed over to the ATF for ballistic testing.
A Mansfield ISD spokesperson said metal detectors are not used at Timberview High School, which is part of the Mansfield Independent School District.
Colby said security had been beefed up at all schools in Arlington and Mansfield. Both cities are near Dallas and Fort Worth.
Colby said the schools were “locked out” so that students could go inside the schools, but no one else could enter. It was not clear how long the security measure would remain in place.
CNN’s Ashley Kilo and Rosa Flores contributed to this report.
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