Updated May 25: Revised to include that Reeves was not under any criminal or disciplinary investigation.

A southeast Texas high school principal shot himself Tuesday afternoon after he notified district officials of his resignation, police said.

Dennis Reeves, 45, killed himself between 4:30 and 5 p.m. while sitting in his pickup at Kirbyville High School, Police Chief Paul Brister said. The truck was in reverse and his foot was on the brake pedal.

Police found a .38-caliber semi-automatic pistol believed to be the weapon, he said. Police are still awaiting an autopsy report that Brister expects to "confirm what we think we know."

This is the truck in which police found Kirbyville Principal Dennis Reeves dead of an apparent self-inflicted gunshot wound to the head. pic.twitter.com/geBKXfMn6q — KFDM News (@kfdmnews) May 24, 2017

The school year ended last week, and Superintendent Tommy Wallis and an assistant superintendent were the only people on campus at the time, according to KFDM-TV.

Wallis, who was hired in March, saw Reeves still in his truck about an hour after he resigned and called police to check on him, Brister said.

Wallis told the Beaumont Enterprise that Reeves said he was quitting to "pursue other interests." He was not being investigated by police or the school district for any reason, Brister and Wallis said.

The Kirbyville school board held an emergency meeting Tuesday night, according to the school website.

Wallis and others reacted to the loss on Twitter.

May God in Heaven put His hands of healing and protection around the community of Kirbyville. pic.twitter.com/D4riugMxNT — Tommy Wallis, Ed.D (@WallisBthe1) May 24, 2017

Prayers for kirbyville and the Reeves family. You were my favorite principal I ever had Mr. Reeves. You will be missed😔🙏🏼 — Victoria (@VictoriaParks_) May 24, 2017

Best Principal to come through Kirbyville. — TJ (@GpcSlim) May 24, 2017

all of my prayers go out to Kirbyville ISD and their community... i can't imagine the pain they're feeling right now 😰💔 — KD (@kenliedavis) May 23, 2017

Staff writer Tom Steele contributed to this report.