03/26/2012 10:21 pm ET

Emily Starnes, Consandra Tyree Charged With Murder Of North Carolina Cab Driver Adam Williams (VIDEO)

Two 16-year-old girls have been jailed in Hickory, N.C., on charges of robbing and murdering a taxi driver last August. If convicted, the girls face life in prison.

Emily Starnes and Consandra Tyree were arrested Saturday afternoon and are jailed without bond at the Catawba County Jail, ABC News reported. The girls were charged on Monday with murder, robbery, conspiracy and firearms offenses in the stabbing death of taxi driver Adam Williams.

"In North Carolina, for criminal court purposes, when you're 16, you're treated as an adult," Hickory Police Department Capt. Thurman Whisnant told "The possibility exists of life in prison, but it's still early to tell."

The charges follow indictments last year accusing Camyron Johnson and Matthew Hopkins on murder and robbery charges, according to WBTV. The station reported that a third man, Robert McElwee, was indicted on one count of accessory after the fact.

Adam Williams had worked for Yellow Cab Co. for a few weeks and had been planning to quit for another job when he was slain. He worked two shifts the night he was killed.

Williams was attacked and stabbed around 10:30 p.m. on Aug. 23, 2011, answering a call at Fuddruckers parking lot, according to the Hickory Record.

Williams, bleeding from slashes to his face and throat, struggled to the door of the nearby LongHorn Steakhouse. Employees called an ambulance to take Williams to Frye Regional Medical Center, where he was pronounced dead.

Officials told ABC News that robbery was the motive. Ronald Stevens, who manages the Yellow Cab Co. in downtown Hickory, said Williams had $39 on him. The money was missing when he was found, according to WSOC-TV.

"It just makes no sense," Stevens told WBTV.

Starnes and Tyree were both arrested on Oct. 5, 2011, and charged with obstruction of justice.

"We knew these two young ladies were involved from the get-go, but wanted to do a complete, thorough investigation," Whisnant told ABC News. "It was clear that they had involvement before, during and after the crime."

Whisnant would not say what role police believe the girls played in the crime. The teenagers are scheduled to appear in court on May 14.