Detectives have started questioning Timothy George Simpkins, 18, who will be charged with three counts of aggravated assault with a deadly weapon, Deputy Police Chief Kevin Kolbye said.
The shooting at Timberview High School left four people injured. Of the four injured, two were shot and three were hospitalized.
The three people hospitalized are expected to survive, Kolbye said. He said a student who is in an intensive care unit is now out of surgery.
An adult male in hospital is in good condition and a woman who could have been grazed by a bullet should be released, Kolbye said.
He said about 1,700 students were at school on Wednesday, and all of them left the building.
The first report of a shooting on the second floor of the school arrived around 9:15 a.m. (10:15 a.m.ET), Arlington Mayor Jim Ross said.
Police said the shooting may have happened after a fight between a student and another person during class.
Authorities launched a “systematic 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 and asked for the public’s help in locating him.
By early Wednesday afternoon, Simpkins was in police custody.
Arlington Police said a gun was recovered from “the streets of Grand Prairie” a few miles from the school.
Grand Prairie Police said the recovered weapon was a .45 caliber handgun.
Chief Daniel Scesney said police believed it was the weapon used in the school shooting, but this has not been confirmed. He said the gun was handed over to the ATF for ballistic testing.
Metal detectors are not in use at Timberview High School, which is part of the Mansfield Independent School District, a spokesperson for ISD from Mansfield said.
Security has been tightened at all schools in Arlington and Mansfield, Kolbye said. The two cities are close to Dallas and Fort Worth.
Kolbye said the schools were “on lockdown” so students could move around the schools, but no one else could enter. it was not known exactly how long this security measure will be in place.
CNN’s Ashley Killough and Rosa Flores contributed to this report.