Hall monitor, 56, shot at Baltimore high school; adult suspect in custody: Officials Students and the remaining staff members are safe, the officials said.

A staff member was shot at a Baltimore high school on Friday, triggering a shutdown of the building, officials said.

The victim, a 56-year-old hall monitor at Frederick Douglass High School, was shot in his lower torso and hospitalized in "serious but stable" condition, police officials said.

The suspect, a 25-year-old man, was a visitor at the high school, according to police officials. Investigators believe the suspect was in the school lobby around noon when he got into an argument with the school employee and shot him, according to the Baltimore Police Department.

The suspect was quickly taken into custody by school police officers who were working in the school at the time of the shooting, according to police.

ABC News' Dee Carden contributed to this report.