Investigators say the man boarded the Route 60 bus at Frankford and Allegheny Avenues last Friday.
There were 30 passengers on the bus when a shootout erupted around 3rd Street and Allegheny in the Fairhill section of the city.
A 17-year-old was critically wounded but is now in stable condition.
Police say the suspected shooter in the new surveillance image was wearing green and black Balenciaga sneakers and a "Supreme" hooded sweatshirt.
Previously released surveillance images show two young men, who police believe are connected to the shooting.
"It's the highest priority to make sure that we are responding to it. For the police, the focus has been on trying to prevent critical incidents like this," said SEPTA spokesperson Andrew Busch.
Officials also said crime on SEPTA buses, trains, and stations is down dramatically this year due to increased patrols and heightened surveillance coverage.
"That includes every bus, every train, every station is covered with surveillance cameras. These give us great pieces of evidence to use in these investigations," Busch said.
SEPTA says overall crime on its properties is down nearly 35% year to date.
Meanwhile, if you recognize the men in those images, please contact the police.
Anyone with information on this shooting or who recognizes the suspects is asked to contact the police.
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