AUSTIN—A single state trooper guarding the Governor’s Mansion the night an arsonist torched the landmark was inadequately trained and ill-equipped to guard the grounds, a Department of Public Safety sergeant investigating the security in place at the time of the fire said Thursday.

DPS Sgt. Michael Escalante told the commission that the one trooper on duty the night of the blaze was not adequately trained to monitor the security system, which was not working properly and required extra vigilance from the trooper. In addition, only 13 of the 20 security cameras on the mansion grounds were operating, he said.

The state fire marshal, who is investigating the fire, has said video footage shows a suspect in the early morning hours of June 8, standing in front of the Governor’s Mansion, igniting an object and throwing it onto the porch of the historic landmark, creating a fireball and blaze that ravaged the 152-year old structure.

The trooper on guard at the time was turned away from the security console in the carriage house behind the mansion and was working on a computer on the other side of the room. Escalante said troopers guarding the mansion are allowed a certain amount of personal time to watch television or use the computer.

An off-duty police officer walking near the mansion at the time of the blaze told the trooper that he had seen a suspicious-looking individual rush away from the mansion area, get in a parked car and drive away, Escalante said. A cigarette lighter found by the officer where the car had been parked has been turned over to the DPS as evidence.