Philadelphia police asked for the public's help in identifying a man wanted in connection with a September murder at a Center City bus stop. 

Southwest Philly resident William Vaughn, 47, died after being stabbed in the chest at 6:42 a.m. while waiting near Broad and Arch streets.

Investigators on Thursday released a video of a suspect in the attack, who was captured on surveillance cameras as he rode the Broad Street Line from the Tasker-Morris Station to Race and Vine. 

The attacker may be homeless, police said. 

The man may have one distinctive feature. He appears to have a protruding lower lip, police said.

Police described the suspect as a black male, in his 40's last seen wearing a gray hooded sweatshirt, blue jacket and tan pants. He was carrying a blue back pack and yellow plastic bag, police said. The suspect was last seen running on foot, northbound on Broad Street from Arch Street towards Race Street.

As with all murder cases, police offered a $20,000 reward for information leading to an arrest and conviction in the case.