The 63-year-old former deputy was killed Jan. 8 during an attempted robbery at an O’Reilly Auto Parts store on Hamilton Mill Road, AJC.com previously reported. Cosme worked at the store after retiring from the sheriff’s office, where he served as a sergeant in jail administration.
Investigators said Cosme was shot while reaching for his gun in an attempt to protect his female coworker. Robertson is believed to have fired the fatal shots.
After Cosme’s death, Gwinnett police teamed up with the FBI and learned the men matched the descriptions of suspects wanted in four previous robberies of Gwinnett County auto parts stores.
Over the course of the investigation, police said Norah and Robertson continued their alleged crime spree, targeting two more stores in Gwinnett, as well as locations in Roswell, Henry County, Athens and Duluth.
The break in the case centered on a Volkswagon Jetta that was used as a getaway car the night Cosme was killed, Gwinnett police spokesman Cpl. Collin Flynn said. Investigators began scouring local surveillance cameras for the Jetta, which they later linked to the two suspects.
A Toyota Camry was also used in the robberies, police said. In December 2019, Roberston was stopped in the vehicle by Braselton police on a suspected DUI charge, according to Flynn. Norah was with him.
Masks and a gun were located inside that sedan during Robertson’s arrest — tools detectives believe were later used in the robbery that left Cosme dead, police said.
While conducting surveillance on the two suspects June 1, a Gwinnett police detective and an FBI agent reportedly witnessed them commit another armed robbery at an Auto Zone in Dacula, police said.
After being confronted, Norah and Robertson took off in a car, authorities said previously.
The vehicle crashed about three miles from the Auto Zone along La Maison Drive. The incident set off a large manhunt in the area.
Norah turned himself in the following morning at the Gwinnett jail. Robertson was captured that afternoon when a tipster spotted him along Old Peachtree and Old Fountain roads.
“After the arrest, detectives were able to locate crucial evidence linking the men to these robberies and the murder,” Flynn said. “That evidence also helped to link them to two other auto store robberies from 2017.”
Robertson and Norah remain held without bond at the Gwinnett jail, online records show.