Detectives have started interviewing 18-year-old Timothy George Simpkins, who will be charged with three counts of aggravated assault with a deadly weapon, Assistant Police Chief Kevin Kolby said.
An Arlington Police Department news release said Simpkins turned himself in without incident and his bond was set at $75,000.
The shooting at Timberview High School left four people injured. Among the four, two were shot and three were hospitalized.
All three hospitalized are expected to survive, Kolby said. One of the victims is a 15-year-old boy with gunshot wounds who is listed in critical condition, according to the release.
A 25-year-old man also had gunshot wounds and is in good condition, the release said. A teenage girl who may have been grazed by a bullet was released Wednesday night and is in good condition with an abrasion, said Arlington Police spokesman Tim Ciesco.
Officials said about 1,700 students were at the school and all have left the building.
The first report of a shooting on the second floor of the school came in around 9:15 a.m. (10:15 a.m. ET), Mayor Jim Ross said.
“The incident occurred in a classroom on the second floor of the school,” the release read. “Investigators believe a physical fight broke out just prior to the shooting.”
Authorities started a “methodical 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 finding him.
By early afternoon, 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 Chesney said police believe it was the weapon used in the school shooting, but that has not been confirmed. He said the gun has been turned over to the ATF for ballistics testing.
Metal detectors are not used at Timberview High School, which is part of the Mansfield Independent School District, a Mansfield ISD spokesperson said.
Security has been increased at all schools in Arlington and Mansfield, Kolby said. Both cities are near Dallas and Fort Worth.
Kolby said the schools were “locked out” so students can move within the schools, but no one else could enter. it was not clear exactly how long that security measure will be in place.
CNN’s Ashley Killough and Rosa Flores contributed to this report.