RICHMOND, Calif. -- One of six men arrested in connection with the gang rape of a 15-year-old girl outside Richmond High School's homecoming dance last weekend will be released and no charges will be filed against him, authorities said Friday.

Contra Costa County Deputy District Attorney Dara Cashman said there was insufficient evidence to file charges against 21-year-old Richmond resident Salvador Rodriguez. He will be released from county jail in Martinez sometime Friday.

Cashman said she had an appointment to meet with Richmond police detectives Monday afternoon to discuss potential charges against a sixth suspect, San Pablo resident Jose Carlos Montano, 18, who was arrested Thursday evening.

Montano was being held in county jail on suspicion of rape, rape in concert with force, penetration with a foreign object and a special enhancement requesting life in prison, Richmond police Lt. Mark Gagan said.

Four other suspects, who include San Pablo residents Cody Ray Smith, 15, and Ari Abdallah Morales, 16; Pinole resident Marcelles James Peter, 17; and Richmond resident Manuel Ortega, 19, have been charged and were arraigned Thursday.

The three juveniles have each been charged as adults with rape by a foreign object while acting in concert. Morales has also been charged with robbery, according to the criminal complaint.

Ortega has been charged with forcible rape while acting in concert, assault with force likely to cause great bodily injury, and robbery.

All four also face enhancements that make them eligible for life in prison.

Smith, the only suspect to enter a plea Thursday, pleaded not guilty to the charges.

The four charged suspects are scheduled to return to court next Thursday.

Police said earlier this week that they believe between seven and 10 people were involved in robbing, beating and sexually assaulting the victim, a Richmond High School student, in front of as many as a dozen onlookers.

Cashman said she decided to charge the juveniles as adults because of the "extremely callous and brutal" nature of the crime.

Detectives believe the attack began around 9:30 p.m., after a classmate beckoned the victim to a secluded area of the campus where she began drinking with them. The assault lasted more than two hours, Gagan said.

The victim was in critical condition when police found her and had to be airlifted to the hospital, police said. She was released from the hospital Wednesday night, Cashman said.

Students, teachers and community leaders held a rally at the high school Wednesday afternoon to speak out against the assault.

Anyone who wants to make a financial contribution to help the victim and her family can send a check to Richmond High School, located at 1250 23rd St., Richmond, 94804-1011. Checks can made out to the Richmond High School Student Fund, sexual assault victim.