Four people accused of robbing an AT&T store at gunpoint in December made off with $23,000 worth of cellphones. But one of those was a phone designed to activate a GPS tracking system, helping police find those responsible, police said Wednesday.

On Dec. 20 at 6 p.m., Peachtree City police were called to the phone store on West Highway 54 for an armed robbery, according to Lt. Mark Brown. Two men, one with a gun, entered the store and left with thousands of dollars worth of phones, Brown said.

Unknown to the store employees and the suspects, one of the stolen phones was actually a “dummy” phone with a tracking system that activated once outside the store, according to police.

“The GPS tracking company notified Fayette County 911, who reported the exact location of the suspects and the cell phones to the responding officers,” Brown said in an emailed statement.

When police found the suspects’ vehicle, the alleged driver, Nakita Burkes, of Atlanta, was arrested. She was charged with armed robbery, according to police.

Tanequa Taylor, of Jonesboro, was later arrested and charged with making false statements, and Ali Faheem, also of Jonesboro, was arrested and charged with two counts of kidnapping and one count of armed robbery, police said.

This week, U.S. Marshals arrested the last suspect, Bryan Roberts, of Rex, Brown said. Roberts was charged with armed robbery.