Two suspects were arrested and third is being questioned in the gang rape of a California teen outside a high school homecoming dance, police said Tuesday.

amd_richmond-hsThe 15-year-old Richmond High School student hospitalized in stable condition after the attack, which happened while as many as 15 people, all males, looked on but didn’t help or call police, investigators said.The sex assault took place on school grounds Saturday while the dance was under way inside the school, authorities said.

“She was raped, beaten, robbed and dehumanized by several suspects who were obviously OK enough with it to behave that way in each other’s presence,” said Richmond police Lt. Mark Gagan.

“What makes it even more disturbing is the presence of others,” Gagan said. “People came by, saw what was happening and failed to report it.” Manuel Ortega, 19, a former student at the school, was arrested soon after he ran from the scene. He faces charges of rape, robbery and kidnapping, and was held on $800,000 bail. “Based on witness statements and suspect statements, and also physical evidence, we know that she was raped by at least four suspects committing multiple sex acts,” Gagan said.

“As people announced over time that this was going on, more people came to see, and some actually participated,” Gagan said. The victim was found unconscious under a bench shortly before midnight Saturday after police received a call from someone who overheard people “reminiscing about the incident,” Gagan said.