Haneef Melton, 19, was taken into custody on Wednesday morning in the 1300 block of Filbert Street in Philadelphia.
The shooting happened in the Lucky 7 store on the 1100 block of Morton Avenue just before 11:20 a.m. on July 2.
Police identified the victim as 27-year-old Dontae Dickerson.
Dickerson was found on the floor of the store with a gunshot wound to the back of the head.
There has been no word on a motive for the shooting.