He came across the body of another man who had been shot to death next to a library in the Logan neighborhood.
Police were called to the scene at Old York Road and West Duncannon Avenue around 1 a.m. Friday.
Investigators say the victim had been shot once in the chest.
Police also found three spent shell casings at the scene near his body.
The victim's identity is not yet known, however, police say he appeared to be in his 30s.
Detectives are scouring surveillance cameras to see if they can help identify the shooter.
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