Police said surveillance video shows Dorsey, who had a gun, and Tate take money from the cash register of the Dollar General store at 4110 Austell-Powder Springs Road on July 27, 2015, about 10 p.m.
The video supposedly shows Dorsey pointing the gun at employees and customers in the store.
Minutes before the robbery, Johnson walked into the store alone talking on his cell phone and acting as a lookout, an investigation found. All three of the men can be seen on video inside the store together earlier that day.
Powder Springs detectives investigated the case and Cobb school police officers identified the young men as having attended McEachern.
“This is an example of solid police work by Powder Springs police with assistance by Cobb Campus Police and the DA’s Gang Unit,” said Vic Reynolds, Cobb’s district attorney, in a statement.
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Cobb Superior Court Judge Tain Kell sentenced the trio immediately after they admitted their guilt in court Friday.
Dorsey and Tate were sentenced to 10 years in prison and five years on probation.
Johnson was sentenced to five years prison time and 15 on probation.
All three have been in custody since September 2015 and will get credit for the time they've already served.
“The law enforcement community in Cobb County will continue to ferret out this gang activity and we will continue to aggressively prosecute these cases,” Reynolds said.