Gwinnett County investigators looking into a string of cellphone robberies at a Beaver Ruin Road apartment complex are asking additional victims to come forward.

The suspect, Zarquavis Nigel Nalls, is already in the Gwinnett County Jail without bond on four counts of armed robbery and seven counts of aggravated assault, police Cpl. Michele Pihera said Tuesday.

“Though he has been charged with these four cases,” she said, “there is a possibility that additional victims have yet to come forward.”

Police believe he is linked to multiple armed robberies, including four that occurred between Jan. 1 and Jan. 6 at the Gwinnett Pointe Apartments in unincorporated Norcross.

All of the victims had a similar story: They posted an ad to sell their iPhones and Samsung smartphones. They were contacted via an app called OfferUp. They agreed to meet the suspect at the 7000 building in the complex. The suspect would point a small black, semi-automatic handgun at them, tell them to leave and keep thier phones.

Police got their break in the case on Jan. 6, when one of the victims watched the suspect walk into the apartment’s 9000 building. The suspect usually wore a tan Tommy Hilfiger jacket with a black hooded sweatshirt underneath, long pants, and tan Timberland style boots, Pihera said.

“Based on the victim’s statement and other evidence found during the follow up investigations detectives were able to execute a search warrant,” she said.

Detectives took Nalls into custody without incident.

Any other victims are asked to call the police department’s robbery unit at 770-513-5378.