Nevertheless, the school spokesman said it's up to parents to make sure their children get safely home from these types of dances.
"Once the child leaves the dance, we don't take them home," Trujillo said.
The spokesman later told KGO, "The dance itself was a success in terms of safety. Nothing happened at the event. We're currently exploring our protocols to make sure that we can expand them, and make sure that this isolated incident doesn't get repeated again."
Police had a different view.
"These suspects are monsters. And, I don't understand how this many people capable of such atrocious behavior could be in one place at one time," Gagan told KGO.
Dara Cashman, head of the Contra Costa County Sex Assault Unit, indicated that witnesses who did not come to the girl's aid or call police were unlikely to be charged with a crime unless they aided the assault.
According to news reports, the girl left the high school's homecoming dance alone around 9:30 p.m. Saturday to get a ride home with her dad.
Instead, she met up with a group of people who were drinking on the edge of campus.
"The series of events that occurred over the next 2½ hours got more severe and more vicious to where she was ultimately gang raped and beaten, and her injuries were so severe that she had to be sent to the hospital in a helicopter," Gagan told KGO.
Trujillo described the mood at Richmond High School is "somber." Counselors and members of the school's crisis team have remained at the school as students -- some who are still not sure who the victim is -- wonder if every absent girl was the one who was attacked.
Trujillo said the school district was not notified officially about the incident until the next morning, though some officials had heard about it on the news.
Trujillo said that school officials had recently approved a "very costly" security system, but that it had not yet been installed. Security cameras already installed in the school are not believed to be functional, he said, but there were no cameras pointed at the spot where the rape happened.
One student, 16-year-old Jennie Steinberg, told the Associated Press that her mother has let her transfer from the school Tuesday.
"It's not safe there at all," she said. "I'm not going back."
Trujillo said 1,688 students attend Richmond High School, which has a banner outside naming it "most improved."