Seven teenage boys were packed into the Toyota Corolla, sitting on top of each other, when the car pulled over on the 1500 block of East Luzerne Street in Juniata Park.
It was about 10:30 Tuesday night, and the youths were looking for a fight, police said.
It had started in school with an argument between some of the friends in the car and three teenage brothers, spilled onto Facebook with threats, and escalated into plans to settle the matter with a physical battle.
As the teens waited in the car, a man in a gray hoodie came out of a house and approached them. Spooked, they drove to the back of the house - but moments later, police said, the same man emerged from the back door and ran up to the passenger side.
He fired from 10 to 12 shots into the car at point-blank range.
Joshua Soto, 14, of North Philadelphia, and Javier Orlandi, 16, of Kensington, were pronounced dead within a half-hour. Dante Lugo, 14, died Wednesday night at St. Christopher's Hospital for Children. The 16-year-old driver was hit in the neck and was listed in stable condition at St. Christopher's.
Police on Wednesday identified the alleged shooter as Axel Barreto, the 30-year-old stepfather of the three brothers, and announced a warrant for his arrest. Barreto was taken into custody about 9 p.m. at the Knights Inn in Bensalem, said Chief Deputy U.S. Marshal John Patrignani.
Barreto, who was with a woman, was not armed and did not resist arrest by Philadelphia police and members of the U.S. Marshals Service Fugitive Task Force, Patrignani said.
Earlier in the day, police described Barreto as "armed and extremely dangerous."
"There very easily could have been seven dead teenagers in that car," Philadelphia Capt. James Clark said. "He just randomly fired."
A search of the car turned up no weapons, Clark said.
Police do not know what sparked the initial argument, which Clark said started between two groups from different neighborhoods.
Asked whether police were concerned that friends of the victims might retaliate, Clark said police would tell the teenagers' schools of the situation and brief officers in their neighborhoods.
Wednesday afternoon, Mayor Nutter visited the schools two of the teenagers attended. At the Kensington Culinary Arts School, where Orlandi was a student until he recently dropped out, Nutter spoke to a group of 75 to 100 students for about five minutes.
The mayor spoke "from the heart," spokesman Mark McDonald said, urging the youths to not retaliate and to focus on their futures.
Next, Nutter stopped by Mariana Bracetti Academy, a charter middle school where one of the non-injured teenagers in the car is a student.
"You are in a great school, in a loving environment, with people who really care about you," Nutter told the students. "Our hearts are heavy about what happened, but we are very concerned about you. Don't let this disrupt what you are about. You need to graduate from the eighth grade, go to high school and on to college.
"Stay in school. Stay positive. Stay focused," the mayor said. "You're doing great work. We just came here to say that we love you and care about you."
McDonald said the mayor felt the need to address the students and "make the case for their future."
"We very seriously hope that they can avoid retaliation or being involved with Facebook fights and the like," McDonald said.