A former reserve deputy in Oklahoma who said he mistook his gun for his Taser when he shot and killed a suspect has been convicted of second-degree manslaughter. Robert Bates, 74, was a volunteer with the Tulsa County Sheriff's Office when he killed Eric Harris during a sting operation in April 2015.

Tulsa World describes the incident, which began with Harris allegedly selling a gun to an undercover deputy, this way:

"As multiple deputies struggled to restrain Harris on the ground after a short pursuit, Bates approached holding a nonlethal weapon in one hand and a lethal one in the other, [Assistant District Attorney John David] Luton reminded jurors."Seeing a small area of Harris' body where he wasn't covered by deputies, Bates announced that he was going to use his Taser and shot a bullet that struck Harris inches from another deputy's head, witnesses testified."

The jury recommended the maximum sentence of four years in prison; sentencing is scheduled for May 31.

NPR's Martin Kaste has reported that some people in law enforcement think the tradition of volunteer policing should end.

"Law enforcement is one of the few professions that allows people to play at the profession," Police Chief Ray Johnson of Chesterfield, Mo., told Martin.

Bates' training and behavior on the job came under scrutiny during his trial, but they had also been the subject of a 2009 internal Sheriff's Office investigation, CBS News uncovered.

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