HARRIS COUNTY (KTRK) --Sunday will mark one year since authorities say a Houston man named Shannon Miles walked up to Harris County Sheriff's Deputy Darren Goforth and killed him execution-style at a northwest Harris County gas station.
Miles is currently in a state mental hospital, where prosecutors say they hope he will regain mental competence so he can stand trial.
When Miles allegedly strode up to Goforth and pulled the trigger 15 times on Aug. 15, 2015, he used a .40 caliber Smith & Wesson handgun, according to witnesses and court documents. A search warrant issued at the time reveals detectives found a gun in Miles' garage matching the bullets recovered at the scene.
A key question remains unanswered: Where did the accused killer get his gun?
A bigger question, perhaps: Where did a man who was declared mentally incompetent years before get this weapon?
SEE ALSO: Eyewitness News goes inside Shannon Miles' mental facility
After a 2012 fight at an Austin Salvation Army facility, Miles was declared mentally incompetent to stand trial, according to court records.
Having been slapped with such a declaration is one of the few reasons you can fail a background check to buy a gun.
No one has been charged with providing him a gun -- and that leaves open the possibility he bought it on his own.
The gun wasn't manufactured until January 2015, Smith & Wesson confirmed to Ted Oberg Investigates.
But if the gun wasn't made until years after he was ineligible to buy one, it encourages even more questions about gun background checks and the mentally ill in one of the most high-profile cases in the area.
Related: Woman claiming to be Goforth's mistress speaks out
"That is a good question and something I will make an issue in this case," Miles attorney Anthony Osso told abc13. "No one in my client's condition should be able to purchase a gun."
The Harris County District Attorney had no comment on where Miles' gun may have come from or any potential crime associated with how he obtained it.
Ted Oberg Investigates will keep pressing for answers, but it may be a question that will only get answered when Miles finally gets to trial.