A fourth person was injured and taken to hospital, Chief William McManus said during a brief news conference, noting that his information was preliminary.
Based on his review of the camera footage, McManus said a San Antonio officer made a traffic stop and had a comfortable conversation with the driver of the truck for a few minutes.
The driver then, for unknown reasons, pulled out a gun and opened fire, hitting the officer in the hand, McManus said.
The officer pulled backwards while firing back, killing both the driver and a passenger and wounding another passenger in the upper body. According to the principal, the person inside the vehicle and the officer fired several rounds.
The principal said he did not know what led the officer to pull the truck.
“He was an officer patrolling here (a wrong stop), which apparently was not that routine,” McManus said.
The killers are believed to be men in their mid to late 20s, McManus said.
The officer, a five-year veteran, was taken to a hospital. McManus said he had no information about his condition other than that he was able to speak.
“I would also say that the officer is very, very happy to be living at that close distance, after being shot in the hand and not being anywhere else more important,” McManus said.