It happened around 1 a.m. Tuesday near the Philadelphia Housing Authority Spring Garden Apartments on the 700 Block of Green Street.
Police were originally called to the scene for the report of a double shooting.
Arriving officers found two men, ages 28 and 56. They were in a courtyard and had both been shot.
Both were rushed to Hahnemann University Hospital.
As investigators were gathering evidence, two neighbors walking from a nearby store discovered the third victim in the grass.
"He was completely unresponsive. He had a gunshot wound to his back," Philadelphia Police Chief Inspector Scott Small said.
He was taken to the hospital where he was pronounced dead shortly before 2 a.m.
Investigators say more than a dozen shots were fired. They believe two gunmen are responsible.
"They are two separate size caliber, so we know two semi-automatic weapons were used," Small said.
Police are hoping surveillance videos will help in the investigation.
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