Raheem Hankerson, 30, of 5812 Lambert Street turned himself in to police on Tuesday after a warrant was issued for his arrest.
Police are still looking for a second suspect - 43-year-old Anthony Burnett. His last known address is in the 2400 block of Nicholas Street.
Investigators say Hankerson and Burnett robbed the A.I. Poland Jewelry Store at 4347 Main Street in the Manayunk section on the morning of March 29th.
About $100,000 worth of jewelry was stolen, along with the store owner's handgun.
Police add that, during the course of the robbery, the store clerk was struck several times in the back of the head with a handgun by one of the suspects. ?He suffered minor injuries and has been released from the hospital.
Anyone with information can contact the Philadelphia Police Department by calling 215.686.TIPS (8477) or visiting the department's website.