Amir Johnson, 19, was taken into custody on North Robinson Street in West Philly, authorities said in a release.
Johnson was one of three suspects named in the June 24 shooting that injured a 5-year-old boy and his grandfather, city police have said.
A man told investigators he was driving along 61st Street with his 71-year-old father and his young son when the occupants of a white car began shooting at them. The man pulled into a gas station where the shooters followed and continued their assault before fleeing west on Passyunk Avenue, according to police.
The 71-year-old victim was hit in the lower back and hospitalized in critical condition while the 5-year-old was grazed along his shoulder and later listed in stable condition, authorities said at the time.
The suspects' vehicle, a white Kia K5, was found abandoned a few blocks north on 61st Street, police said. It had previously been reported stolen in a robbery at the Philadelphia International Airport.
The other two suspects, Antwan Grimes and Keon Smith, were arrested last July and September respectively, court records show.
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