A Mattapan man was arrested on robbery charges in a sting operation planned by the victim’s younger brother and Boston police, authorities said.

Jordan Searcy, 18, was arraigned in Dorchester District Court on Tuesday and pleaded not guilty to charges of armed robbery, assault with a dangerous weapon, and conspiracy, said Suffolk District Attorney Daniel F. Conley. Searcy is required to wear a GPS device if released on his $1,000 bail.

Last week, a 20-year-old Woburn man arranged the purchase of a cellphone over Facebook, prosecutors said. A Facebook user that police believe to be Searcy, although he was under a different name, agreed to sell the phone for $300, said Conley’s office.

Advertisement - Continue Reading Below

On the evening of Feb. 16, the victim and and his 18-year-old brother went to a pre-arranged meeting location in an alley off of River Street in Mattapan. They were allegedly robbed at knifepoint by Searcy and another man, prosecutors said.

Boston police were unable to find the suspects in the area, Conley’s office said.

The younger brother used Facebook to coordinate a similar sale with the same man on Monday, meeting in the same alleyway. A police detective acted as the buyer, according to Conley’s office.

As Searcy and a second suspect approached, the victim’s brother identified Searcy from the previous robbery, said Conley’s office.

Searcy and the other man ran into a building, with Searcy later emerging in a unconvincing disguise, prosecutors said. Police took Searcy into custody, but his unidentified companion escaped, according to Conley’s office.