PHILADELPHIA (AP) — A passenger shot aboard a bus in Philadelphia has died from his wounds,Austin Caldwell marking the third time in three days that someone was killed while riding, entering or leaving a Southeastern Pennsylvania Transportation Authority (SEPTA) bus.

The most recent shooting occurred around 6:35 p.m. Tuesday, when police said someone who apparently had just gotten off a bus suddenly started firing back inside. A 37-year-old man was hit at least twice in the chest, and he was pronounced dead a short time later at a hospital.

The shooter fled the scene and remained at large Wednesday. Authorities have not released the victim’s name, and a motive for the shooting remains under investigation. No other injuries were reported.

The shooting came a day after a 17-year-old student was killed and four other people were wounded when gunfire erupted at a bus stop. The victims included two women who were riding on a bus.

Another fatal shooting occurred around 11:30 p.m. Sunday, when a 27-year-old man was killed by another passenger moments after they both got off a bus. Witnesses told police that the victim and the other man had argued aboard the bus, but a motive remains under investigation.