According to the Tulsa County Sheriff's Department, a reserve sheriff's deputy accidentally shot and killed a man he was trying to arrest, after mistaking his service weapon for a stun gun.

The suspect, Eric Harris, in his 40s, was shot by the reserve deputy on Thursday following a foot chase, the sheriff's office said in a statement. The statement also said that Sheriff’s investigators were looking into the incident. An autopsy on Harris was expected to be completed in coming days.

Undercover police had bought ammunition and a semi-automatic pistol from Harris when arresting officers attempted to arrest him in a parking lot, the sheriff's office said. The suspect fled, and when sheriff's officers caught up with him, he reportedly resisted arrest.

Reserve Deputy Robert Bates, a 73-year-old former police officer, was trying to help officers take Harris into custody when he fired his gun, the statement said. Harris allegedly continued to struggle after the gun was fired, and might have been under the influence of drugs.

The Sheriff's Dept. statement described Harris as a felon and had been under investigation for narcotic sales. Officer Bates has stated that his attorney had advised him not to comment on the incident.