Oklahoma reserve deputy pleads not guilty to manslaughter in shooting black man
Tulsa County reserve sheriff's deputy Robert Bates appears on NBC's 'Today Show' on April 17, 2015.

An Oklahoma reserve deputy pleaded not guilty to second-degree manslaughter on Tuesday for killing a black man he said he accidentally shot with a gun instead of a Taser, a Tulsa County District Court clerk said on Tuesday.

A series of fatal shootings by police of African Americans, often unarmed, has fueled a national debate about police treatment of minorities, and resulted in angry demonstrations and unrest in various parts of the United States.

There have been protests in Chicago after a judge found a police officer not guilty of involuntary manslaughter for the killing of 22-year-old black woman on Monday. The officer is Hispanic.

Robert Bates, 73, an insurance executive who serves as a volunteer deputy with the Tulsa County Sheriff's Office, shot and killed Eric Harris, 44, on April 2.

He was trying to help officers subdue Harris, who had fled after allegedly trying to sell a gun illegally to an undercover officer.

Bates could face two to four years in prison if convicted.

"We believe he has a defensible case," Bates' attorney, Corbin Brewster, said in a telephone interview.

USA Today reported that the court judge allowed Bates to take a planned vacation to the Bahamas before his upcoming July court date.

"At a time when we are still mourning the death of a loved one that he shot down in the street, Mr. Bates will be relaxing and enjoying his wealth and privilege," the Harris family said in a statement to the paper.

On Friday, Bates apologized to Harris' family in an interview on NBC's "Today" show, saying he mistakenly fired his gun instead of his Taser.

Bates said the portrayal of him as a close friend of the sheriff who was rewarded for his financial support with the law enforcement position is "unbelievably unfair."

Tulsa County Sheriff Stanley Glanz apologized on Monday to Harris' family and acknowledged a long-time friendship with Bates, who he said had been his insurance agent.

Glanz defended Bates' training record and qualifications, and his involvement in the operation. Glanz denied Bates' training records were falsified and said the office was looking for missing documents and would release them as they are found.

The sheriff also said two deputies involved in the incident have been reassigned after receiving threats and the department would review national standards for reserve officers.

(Reporting by Heide Brandes in Oklahoma City and Suzannah Gonzales in Chicago; Writing by