HOUSTON (AP) — A former student of a Houston charter school shot and wounded a school employee on campus Friday morning before quickly surrendering to police, authorities said.

The man shot through a locked, glass door at YES Prep Southwest Secondary, then shot the employee in the back, Houston Police Chief Troy Finner said.

The employee was in serious condition at a hospital, Finner said. No students were hurt, the school said in a statement.

Police did not release the name of the wounded employee or the shooter but said they were able to quickly identify him because he was a former student. Police also did not release a motive, but Finner said authorities were investigating whether the shooter and wounded man had any past interactions.

The shooting happened at about 11:45 a.m. YES Prep Southwest Secondary is a charter school that serves students in sixth through 12th grades.

A line of students in masks streamed out of the school just before 1 p.m., holding their hands up to show officers they were not carrying a weapon. Multiple students told reporters in Spanish and English what they witnessed. Some said they saw blood while leaving the building, and others said they hid and blocked doorways with furniture like they had practiced in drills to survive a shooting.

Parents could be seen having tearful reunions as they met their children in a parking lot near the school.

“You don’t want anything like this to happen,” Finner said, “but I want to commend those students. Every student I’ve seen coming out, they were calm. The administrators, the teachers, outstanding job. I want to commend them. ... They train for it.”

The shooting Friday happened about 30 miles (50 kilometers) from the site of one of the deadliest school shootings in U.S. history. A then-17-year-old armed with a shotgun and a pistol opened fire at Santa Fe High school in May 2018, killing 10 people, most of whom were students. The suspect has been receiving mental health treatment at a state hospital since December 2019. Doctors say he remains incompetent to stand trial on state capital murder charges. He also faces federal charges in a sealed criminal case.