UPDATE: Philadelphia Police identified the suspect as Steven Simminger and victim as Colin McGovern. They say the incident appeared to begin as a verbal fight over Simminger's New Jersey Devils baseball cap.

Police arrested a homeless veteran accused of stabbing and killing a man in downtown Philadelphia's Rittenhouse Square neighborhood after what witnesses described as an argument over sports teams.

Police said they responded about 3 a.m. for 9-1-1 calls about a person with a weapon and a stabbing at 19th Street and Rittenhouse Square. The victim, a 24-year-old man from Bucks County, was walking with another man and two women when they were approached by a man they did not know, investigators told NBC10's Monique Braxton.

Braxton learned at the scene that the victim and the attacker argued over sports teams briefly before the attacker pulled a knife and stabbed the man in the stomach.

Good Samaritans and the victim's friends rushed to help him, taking off articles of clothing to try to stop the bleeding.

"I took my jacket off, I knelt down beside him, lifted his shirt up and just started putting pressure on what was a stab wound that we saw on his stomach," Megan Hellander, one of those Samaritans, said. "And I was just trying to kind of whisper in his ear that the ambulance was coming."

Police said it appears that the man did not know the assailant and that he and his friends were approached by the person at random.

"There was a brief verbal altercation, a struggle ensued that lasted a few seconds, and by witness accounts, the offender stabbed the complainant," Philadelphia Police Capt. Nicholas Smith said at the scene. "Then [the attacker] fled the area going southbound on 19th Street, then eastbound on Manning Street."

Sunday night, police told NBC10 they arrested a suspect in the deadly stabbing. While they did not release his name, they said he is a homeless veteran who frequently stays in Rittenhouse Square. A source told NBC10 he went to the VA Hospital on Woodland Avenue because he was injured during a scuffle before the stabbing. Police told NBC10 they were able to identify him through surveillance video.