Police said on Monday that Shannon Miles, 30, who is accused of shooting and killing Harris County Sheriff’s Deputy Darren Goforth, has a history of mental illness, the Associated Press reports. After an arrest in 2012, he was sent to a state mental hospital for several months.

According to the AP, Miles, charged with aggravated assault with a deadly weapon after getting into a fight at a homeless shelter over a remote control, was found to be mentally incompetent in October 2012. He was sent to North Texas State Hospital in Vernon, Texas. There, in February 2013, he was declared mentally competent—prosecutors at the Travis County District Attorney’s Office offered him a plea agreement of seven years in prison—but the charge was dropped when the victim could not be found.

Miles is charged with capital murder and is being held without bond. In a court hearing on Monday, Harris County District Attorney Devon Anderson said Miles ambushed Goforth and shot him 15 times:

Surveillance video from the gas station showed the 10-year law enforcement veteran had just come out of a convenience store when Miles got out of his red truck, she said. “He runs up behind Deputy Goforth and puts the gun to the back of his head and shoots. Deputy Goforth hits the ground and then he continues to unload his gun, shooting repeatedly into the back of Deputy Goforth,” Anderson said.

Goforth was shot 15 times, Anderson said, and shell casings match the .40-caliber Smith and Wesson handgun found at Miles’ home. Miles’ next court date is Oct. 5.

The killing evoked strong emotions in the area’s law enforcement community, with Hickman linking it to heightened tension over the treatment of African-Americans by police. Goforth was white and Miles is black.

Anderson refused to speculate about Miles’ motive. Asked whether it had anything to do with the aforementioned heightened tensions, Anderson said, “I have no idea whether it does or not.” Authorities said there is no evidence that Goforth and Miles knew each other.

One of Miles’ two court-appointed attorneys, Anthony Osso, told the AP that his client means to plead not guilty.

Photo credit: AP Images. Contact the author of this post: brendan.oconnor@gawker.com.