PHILADELPHIA (AP) — A 17-year-old who was in a car stopped for an expired car registration sticker traded gunfire with police during a Tuesday morning highway chase that ended with a fiery crash involving a school bus and a trooper with a gunshot wound, police said.Trooper Patrick R. Casey suffered a “flesh wound” to his shoulder, state police Capt. James Raykovitz said.The teen and a second person who was in the car when it was stopped were in custody as police searched for two more people following the midmorning crash on a downtown highway, authorities said.When police first stopped the car, they asked the four people inside to exit the vehicle, but one of the suspects jumped back in and took off, investigators said.Trooper Patrick R. Casey, providing backup, pursued the car, at one point getting in front of it to try to force a stop, authorities said. The suspect instead rammed Casey’s cruiser, then pulled alongside him and opened fire, Raykovitz said.The suspect then crashed into the school bus, causing both vehicles to burst into flames. The bus was empty except for the driver, who escaped unharmed.