BRENTWOOD -- A middle-school boy could face criminal charges for allegedly forcing a girl into sexual acts after he received sexually explicit photos of her on his cellphone, and several other students at four middle schools are under investigation for exchanging inappropriate images, police said.

On Monday morning, Brentwood police were called to Adams Middle School on American Avenue to investigate a report that students there were exchanging images of themselves in various stages of undress, police said.

A preliminary investigation showed several students between ages 12 and 14 from three Brentwood schools and one Byron school had used their cellphones or other electronic devices to send and receive the pictures. The schools were Adams Middle School, Bristow Middle School and Edna Hill Middle School in Brentwood and Excelsior Middle School in Byron.

One boy reportedly used an incriminating picture of a girl to force her into sexual acts.

"I am saddened to hear the serious nature of what has happened," said Heather Partida with the Brentwood Union School District. "Student safety is our number one priority and I am thankful the police were able to come in quickly and begin to sort out this situation. I know this led me personally to have a serious conversation with both of my daughters about being safe and making good choices."

Partida added that she is looking forward to having both the school and the police department reinforcing Internet safety and the dangers of cyberbullying to both students and parents.Students found with the pictures were disciplined by school administration.

Brentwood police are working with the Contra Costa County District Attorney's Office, which will review the cases and determine if criminal charges will be filed.

During the past year, Brentwood detectives have worked with school administrators in the nearby Liberty Union High School District to educate parents and community members on teen cyberbullying, Internet safety, cellphone use and the dangers of "sexting." Additional information on cellphone and Internet safety can be found at netsmartz.org.

The investigation is ongoing, and anyone with information regarding the case is asked to call police detectives at 925-778-2441 or 925-634-6911.

Follow Kristin J. Bender at Twitter.com/kjbender.