amphotora/iStockBy IVAN PEREIRA, ABC NEWS

(BROWARD COUNTY, Fla.) -- One of the officers who was fired over his handling of the 2018 Parkland, Florida, high school shooting will get his badge back.

Sgt. Brian Miller will receive full back pay and seniority when he returns to his duties at the Broward County Sheriff’s Office, the Broward Sheriff’s Office Deputies Association Union said Wednesday.

Miller was one of two officers who were fired last year after an investigation deemed they had "neglected their duties" when they responded to the Feb. 14, 2018, shooting at Marjory Stoneman Douglas High School that left 17 dead and 17 injured.

An internal investigation found that Miller, who was the first supervising officer who responded to the scene, hid behind his car while shots rang out inside the high school. The union said an arbitration ruled the "BSO violated Sgt. Brian Miller’s Constitutional due process rights and improperly terminated him."

Union leaders were scheduled to hold a news conference Thursday to provide more details about the ruling.

The sheriff's office didn't immediately respond to ABC News' request for comment.

The Florida Sun-Sentinel first reported Miller's reinstatement Wednesday. The paper said the officer made $137,000 in 2018.

Florida Gov. Ron DeSantis fired Sheriff Scott Israel for his handling of the shooting and replaced him with Gregory Tony.

Broward County Sheriff’s Office Deputy Scot Peterson, who was assigned to the school, also lost his job last year and was charged with child neglect charges after an internal investigation found he retreated and took cover when the shots rang out.

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