The shooting on Wednesday morning began after a fight broke out in a classroom and a student opened fire, authorities said. The suspect, identified as 18-year-old Timothy George Simpkins, fled the scene and was taken into custody hours later.
Journalist Nerissa Knight shared a video on Twitter allegedly captured by one of the students during the incident.
"My daughter just texted me that there was a school shooting at Timberview HS ... She sent this video that’s out. Her nearby school is on lockdown also, and we hear police sirens rushing in. Police confirm there is an active shooter. Praying," she wrote.
Another video making rounds on social media showed the scuffle between the accused and another student that allegedly led to Mr Simpkins opening fire.
A woman, likely the teacher, can be seen screaming "I need help" and "what are you doing" during the fight.
Arlington police confirmed that the video circulating on social media appears to have been recorded inside Timberview High School. However, assistant police chief Kevin Kolbye said he was not “100 per cent sure” if the video was taken on Wednesday.
“All I know is I saw that video, and that was what was presented to me,” he was quoted by Dallas Morning News as saying.
Among the victims who suffered gun shot wounds, a 15-year-old male was in critical condition. A 25-year-old man and a teenage girl were described as being in a good condition. The fourth victim was treated at the scene.
Mr Simpkins was taken into custody and charged with three counts of aggravated assault with a deadly weapon. According to the police, the accused communicated with his attorney before turning himself in and has been booked into the Arlington City Jail.
A .45 calibre handgun, used during the shooting was recovered from England Parkway in Grand Prairie.
Following the incident, the Mansfield Independent School District wrote to parents to say the school is in lockdown and police are investigating an “active shooter situation.”
However, just after midday, the school district gave an “all clear” sign to say the immediate danger was over. Students and staff who were locked inside their classrooms and offices were being “safely escorted to buses,” the school district told parents.