The execution-style killing of a Philadelphia man who was speaking to a political candidate about volunteering for his campaign led to a retaliatory shooting that left one teenager dead and another wounded, police said late Sunday.

"We do believe these are two rivaling factions,' Philadelphia Police Commissioner Richard Ross told reporters. "What they're fighting over we haven't pinned that down right now, but we are not going to let this pass us by, by not assuming that it's gang related because everything suggests that it is."

The first shooting took place at around 3:30 p.m. in the Cedarbrook section of the city. Witnesses said the unidentified 21-year-old victim was talking with Chris Rabb, a Democratic candidate for the Pennsylvania House of Representatives when someone approached the victim from behind and shot him. 

Chris Visco, Rabb's campaign manager, told Philly.com the victim had told Rabb he was going to be a poll worker during Tuesday's primary election, but also expressed interest in volunteering for Rabb's campaign. Visco added the victim died with a piece of Rabb campaign literature in his hand. 

"One of the people that was with (Rabb) handed him a piece of literature, took his phone number, and another young man came up behind him and shot him execution style in the head," Visco told WPVI.

Police say the victim was pronounced dead at the scene. Rabb was able to pull his volunteer to safety in a nearby convenience store. They were not injured.

The second shooting took place at approximately 7:30 p.m. about a quarter-mile from the scene of the first shooting. Police said an 18-year-old man was shot in the back and a 17-year-old boy was grazed by a bullet in a drive-by shooting. The 18-year-old was taken to a hospital, where he later died. The 17-year-old was expected to recover.

No arrests have been made in either shooting. Police described the suspect in the afternoon killing as a black man standing approximately six feet tall and wearing a light gray hoodie. He was seen running from the scene. 

As in the first shooting, police did not release the names of the victims in the later shooting. It was not immediately clear whether either victim was a suspect in the first shooting.

"I'm somewhat exasperated by this," Ross told reporters Sunday night. "It speaks to what we deal with across this city and [in] cities across the nation, with retaliatory violence, and the manner [in] which particularly young people handle their grief, and their retribution. And it's ridiculous."

The Associated Press contributed to this report.

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