(CNN) -- Police arrested another teen Thursday, the sixth suspect jailed in connection with the gang rape of a 15-year-old girl on a northern California high school campus.

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

Montano was arrested Thursday evening in San Pablo, California, a small town about two miles from the city of Richmond, where the crime took place.

Montano, who was held in lieu of $1.3 million bail, is accused of taking part in what police said was a 2½-hour assault on the Richmond High School campus.

Police said as many as 10 people were involved in the rape in a dimly lit back alley at the school, while another 10 people watched without calling 911.

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

Four other teenage suspects were arraigned Thursday on charges connected to the rape.

Cody Ray Smith, described by the court as older than 14, pleaded not guilty to charges of rape with a foreign object and rape by force.

Two other juveniles, Ari Abdallah Morales and Marcelles James Peter, appeared with Smith at the Contra Costa County Superior Court, but did not enter a plea. The court described Morales as younger than 16, and did not give an age for Peter.

All three juveniles, who wore bulletproof vests at the hearing, were charged as adults.

A fourth person, Manuel Ortega, 19, appeared separately without an attorney and did not enter a plea. He did not wear a protective vest.

Another person, Salvador Rodriguez, 21, was arrested Tuesday night, but he was not in court Thursday.