(Reuters) – A police officer wounded during a shooting incident inside a high school in Knoxville, Tennessee, was struck by a bullet that was not fired by the gun of the student who police shot and killed, according to a preliminary investigation.

A 17-year-old high school student, who opened fire at an Austin-East Magnet High School, was fatally shot on Monday during a confrontation with the police.

The officers, who were responding to the scene, tracked the gunman to a bathroom where shots were fired. The student died at the scene, and police initially said the wounded officer had been hit when the student opened fire on them.

“Preliminary examinations indicate the bullet that struck the KPD (Knoxville Police Department) officer was not fired from the student’s handgun,” Tennessee Bureau of Investigation said in a statement Wednesday.

TBI said student fired first, and the officers fired back.

The wounded policeman, Adam Willson, was serving as a school resource officer. Having been shot in the upper leg, Willson was in a serious condition following surgery, but was said to be recovering on Tuesday.

Investigators declined to say whether the bullet that struck Willson came from his own gun or from another officer’s weapon, according to the New York Times.

TBI was not immediately available to Reuters’ request for comment late in U.S. hours.

The findings of the investigation, which is active and ongoing, will be shared with the District Attorney General.

(Reporting by Aakriti Bhalla in Bengaluru; Editing by Simon Cameron-Moore)