Police have arrested a sixth suspect in the homecoming gang rape of a 15-year-old girl on a high school campus in Richmond, Calif., officials say.

Jose Carlos Montano, 18, was arrested on charges of felony rape, rape in concert with force, and penetration with a foreign object, Richmond Police Lt. Mark Gagan told CNN.

Montano was accused of taking part in what police said was a 2 1/2-hour assault at the school. Police said as many as 10 people were involved in the rape in a dimly lit back alley while another 10 stood by and watched.

The victim was taken to the hospital in critical condition but was released Wednesday.