The North Little Rock Police Department said Wednesday that two additional suspects were arrested in the murder of an airman who tried to foil a gas station robbery last week in Arkansas.

Darrius Stewart, 17, and Keith Keshawn Harris, 16, have both been arrested and charged with capital murder and aggravated robbery, the police department said in a Twitter post Wednesday. Both are being charged as adults in the death of Senior Airman Shawn McKeough, who was assigned to Little Rock Air Force Base in Arkansas, Little Rock police said.

Police previously said they had arrested 18-year-old Drequan Robinson and 18-year-old Keith Harris Jr., who is Keith Keshawn Harris’s brother. They were also charged with capital murder and aggravated robbery.

Stewart and Robinson are accused of entering the Valero Big Red gas station and convenience store, about 13 miles southwest of Little Rock Air Force Base, at about 11:38 p.m. March 15 and tried to rob it. A probable cause affidavit filed in district court said McKeough tackled one of the robbers, before the second shot him in the head and killed him. Robinson is accused of being the robber who killed McKeough.

Keith Keshawn Harris is accused of being the driver of the vehicle that waited outside. The North Little Rock police said Keith Harris Jr. admitted to being a passenger in the vehicle and being aware the robbery would occur.

The police also said Stewart had confessed to going into the Valero and participating in the robbery.