Miami-Dade jailers were stunned when they found a gun in the shoe of inmate Santos Mejia as they were booking him this week.

The .22-caliber handgun was taken from Mejia and given to Miami officers. Mejia was being booked on charges of aggravated assault with a firearm and aggravated battery with a firearm. An additional charge of bringing contraband into a jail was filed against him for possession of the .22 in his shoe.

Miami police are investigating why veteran patrol officer Emilio Valenzuela failed to find the gun before turning Mejia over to the jailers.

Mejia is reportedly a Honduran laborer with no previous arrests in Florida. He was arrested Friday night and charged with shooting Juan Carlos Flores, 34, in the right leg on Sept. 8.

Miami police policy states that “Officers must search prisoners prior to placing a prisoner in a police vehicle. It cannot be assumed that the prisoner is free of weapons or contraband—even if previously searched.”

Officer Valenzuela’s sergeant will investigate the matter, according to Lt. Bill Schwartz of the Miami PD. He told the Miami Herald that the failure to find the gun was a training lapse.

“It’s very rare that officers, up until now, would ask a prisoner to take off his shoes,” Schwartz said. “We live and learn and, as a result, you’ll be seeing that done routinely.”