(CNN) -- A seventh person has been arrested in a gang rape on a high school campus in northern California, police said Tuesday.
Richmond Police Lt. Mark Gagan did not identify the suspect. Of those arrested so far, one was released for lack of evidence.
Police say as many as 10 people were involved in the rape October 24 in a dimly lit alley outside Richmond High School, where a homecoming dance was taking place.
Another 10 people watched the attack without calling 911, police say.
Authorities say the attack lasted for more than two hours. The victim was taken to the hospital in critical condition, and was released Wednesday.
The victim's parents issued a statement that urged those in the community to work to ensure that such an attack never happens again.
"If you need to express your outrage, please channel your anger through positive action," they said, according to the Rev. Jim Wheeler, who said he was the family's pastor at First Presbyterian Church in Richmond.
CNN's Dan Simon contributed to this report.