First on CNN: Texas DPS trooper arrived on scene of Uvalde school shooting earlier than previously known, body cam shows

(CNN) Body camera footage released by the city of Uvalde last month shows a Texas Department of Public Safety trooper was on the scene outside Robb Elementary School just 2 minutes and 28 seconds after the gunman entered, a timeline earlier than previously known.

The department had only disclosed, in timelines and testimony, that the first state trooper entered the school hallway at 11:42 a.m., nine minutes after the gunman entered the school. But DPS had not stated when the trooper first arrived at the school itself.

The more specific timeline raises further questions about DPS's own transparency and role in the botched police response, even as the department leads the investigation into what happened. The body camera video was provided to CNN by Uvalde Mayor Don McLaughlin, who has expressed his frustration with the department's investigation and accused DPS of a "cover-up."

The head of the largest police union in Texas said the new timeline raised serious questions about the department's trustworthiness.

"I don't know that we can trust them to do an internal investigation," Charley Wilkison, the executive director of the Combined Law Enforcement Associations of Texas, which represents some law enforcement officers in Uvalde, told CNN on Tuesday. "It would be best if the investigation were headed up by an outside independent source that the public can have total confidence in.