LOS ANGELES — Two people in a black BMW on Monday ran a red light, hit and killed a pedestrian and broadsided a school bus that flipped on its side, leaving the bus driver and 18 high school students injured.

The two people fled on foot from the busy intersection in Boyle Heights, east of downtown Los Angeles, and were caught by a construction worker, who held them until police arrived and detained them, Police Chief Charlie Beck said at a news conference.

The bus driver was taken to a hospital in critical condition but later was upgraded to serious condition, authorities said.

Eighteen high school students on the bus also were taken to hospitals with non-life-threatening injuries.