Police say the suspect stabbed a man in his 30s multiple times around 3:15 a.m. Thursday.
The victim was taken to the hospital where he later died.
The suspect is described as a heavy-set black man, wearing a white T-shirt, blue jeans and red sneakers. He was also seen carrying a dark-colored backpack.
The entrance at 10th and Filbert was closed while police investigated. It has since reopened and all Regional Rail service is operating on or close to schedule.