Corey White, 22, was shot in the 5100 block of Hadfield Street around 7:45 p.m. He was pronounced dead at the Hospital of the University of Pennsylvania.
At a news conference on Tuesday afternoon, police said it began when two men pulled up to White in a car.
"The preliminary investigation reveals that the occupants of a brown vehicle pulled up on the decedent, got out, there was some type of verbal confrontation -- and one of them pulled out a gun and shot him once in the chest," said Philadelphia Police Captain James Clark.
Police say the car used in the murder had been stolen from 69th Street Station during the day and was found on fire in Yeadon, Pa.
There was also no immediate word on if White's killing had anything to do with the alleged plot.
"There are a couple of other theories out there," Philadelphia Police Captain James Clark said during the news conference.
However, White's death came just hours after a judge upheld charges against the two suspects, including the mother of his baby.
That woman, 20-year-old London Eley, is accused of posting a message on Facebook that offered $1,000 to anyone who killed White.
A defense lawyer argued that Eley was only venting when she posted the online message after an argument with White.
Police say 18-year-old Timothy Bynum, of suburban Darby, accepted the offer and asked for details about the target.
"I will pay somebody a stack to kill my baby father," Eley wrote in a post this spring, according to a police affidavit.
"Say no more ... what he look like ... where he be at ... need that stack 1st," Bynum wrote back, police say.
Eley exchanged messages with Bynum for about an hour but never met him or took any other steps to carry out the plan, according to her lawyer, Gerald Stein.
A city judge on Monday approved a murder solicitation charge and a weapons charge - with the computer being considered the weapon - against Eley and approved murder conspiracy and weapons charges against Bynum. Police say they found several weapons in Bynum's home, although Stein said he believes one was lawfully licensed to a parent and another was a BB gun.
Both defendants remained in custody Monday, with bail reduced from $50,000 to $35,000 for Eley and from $75,000 to $50,000 for Bynum. They are due back in court for arraignment on Sept. 6.
His family apparently learned of the posts and contacted police, who arrested Eley and Bynum in June.
Stein said Eley simply had been venting online "over an argument that she had with the boyfriend."
"And then, after an hour, she calmed down. End of story," Stein said. "Well, when you do it on a computer, you are putting it out there for the whole world to see and memorializing it. Unfortunately, it sort of magnifies the anger."
However, a prosecutor said Eley was asked online if she was joking about the hit and insisted she wasn't.
"It is a unique case," Assistant District Attorney Jack O'Neil said. "I think the judge made the right decision, and we're going forward from here."
Bynum's lawyer, Lopez Thompson, did not immediately return messages from The Associated Press seeking comment on Monday.
The Associated Press contributed to this report.