The Dallas Police Department is launching an internal affairs investigation following allegations of evidence tampering during the murder trial of former DPD officer Amber Guyger. Jurors convicted Guyger on Tuesday and sentenced her to 10 years in prison Wednesday.

"Dallas today is different than it was yesterday and definitely different than it was a year ago," DPD Chief U. Renee Hall said Wednesday night.

During the trial, DPD Sgt. Breanna Valentine said that DPD Sgt. Mike Mata, the president of the Dallas Police Association and Valentine's superior officer by virtue of service time, told her to turn off the in-car camera system that was filming Guyger as she sat in a police vehicle after shooting and killing Botham Jean.

Turning off the camera was not normal police procedure, Valentine said.

"What you saw and heard was disheartening, and I can only imagine the public's perception of who we are as a police department," the chief said.

Despite calls from activists for his resignation, Mata said Wednesday that he'd done nothing wrong.

“I welcome it and want a thorough investigation of all parties who were at the scene that night,” Mata told The Dallas Morning News. "And when this investigation is done, it will show that I violated no policy and I did the standard practice that has been in place for several years.”

EXPAND Mike Mata, president of the Dallas Police Association, is under fire for his behavior following the Amber Guyger shooting. Jim Schutze

"The testimony that came out in this trial is not reflective of the men and women in the Dallas Police Department," Hall said.

Martin Rivera, Guyger's DPD partner and former lover, admitted at trial that he deleted text messages from Guyger in the aftermath of the shooting. Internal affairs will also investigate Rivera, who remains employed by the department, Hall said.

"We're not backing away from those things," Hall said. "As a department, we're always assessing ourselves."

Hall emphasized that it was the Texas Rangers, not the DPD, that led the investigation into the murder.

"The Dallas Police Department is not what you've heard over the last week and a half," Hall said.