The number of people arrested in the gang rape of a 15-year-old girl outside a high school dance in Northern California has increased to six and could get higher, authorities said.

Jose Carlos Montano, 18, was arrested Thursday evening outside his San Pablo home. He was being held on $1.3 million bail, on suspicion of rape, rape in concert with force and other charges, Richmond police said.

Authorities were still looking for suspects, and have said as many as 10 people ranging from 15 to the mid-20s may have attacked the girl for more than two hours Saturday in a dimly lit area.

Montano's arrest came after three other teen suspects appeared in court for the first time Thursday.

Cody Ray Smith, 15, pleaded not guilty, while Ari Abdallah Morales, 16, and Marcelles James Peter, 17, did not enter pleas during their arraignment in Contra Costa County Superior Court.

Smith, Morales and Peter each were charged with rape in concert and sexual penetration with a foreign object. They were being held without bail and could be eligible for life in prison, if convicted.

The three were charged as adults because of the severity of the crime, prosecutor Dara Cashman said.

Another suspect, 19-year-old Manuel Ortega, was arraigned separately but did not enter a plea. He is charged with rape, robbery and assault causing great bodily injury, and is being held on $1.2 million bail.

Salvador Rodriguez, 21, also remained jailed but has not been charged.

Peter's aunt, Monica Peter, said before Thursday's hearing that her nephew told her he was only a bystander and didn't participate in the attack. She said he didn't do anything to stop the attack because he feared "he would get his ass kicked."

Morales' attorney, Ernie Castillo, said he was still learning details about the case and didn't know "what limited role, if any," his client played in the attack.

Cashman said her office has received numerous calls and e-mails about the case, mostly "expressions of outrage from all over the country."

Police said the victim left the homecoming dance at Richmond High School and was walking to meet her father for a ride home when a classmate invited her to join a group drinking in the school courtyard. The girl had consumed a large amount of alcohol by the time the assault began, police said. Her father tried to call her cell phone, but no one answered.

Police said they received a tip about a possible assault on campus from a former student, who heard two males bragging about it. Officers found the girl semiconscious and naked from the waist down near a picnic table.

Authorities have said as many as two dozen people watched the attack without calling police.

The girl was released from a hospital Wednesday.

More coverage at KTVU.com.