Investigators believe Lemel Groce, 18, and two other men flashed a gun at a 15-year-old boy in the Brighton neighborhood of Seattle before snatching his necklace and fleeing.
The alleged armed robbery occurred last week.
Groce, who goes by the street name “Lil’ Soup,” was booked into the King County Jail just before 5 a.m. Wednesday.
Officers said they chased down one of Groce’s accomplices. They then turned the case over to robbery detectives, who have since identified Groce as one of the other suspected robbers.
Police said he is a professed gang member.