(CNN) -- An HIV-positive former Maryland school aide and track coach has been arrested on suspicion of sexually assaulting several students and recording some of the abuse on video, including on school property, authorities said.
Carlos Deangelo Bell, 30, of Waldorf is accused of assaulting at least seven boys, mostly of middle school age, Charles County Sheriff's Office spokeswoman Diane Richardson said.
Bell was arrested at his home Friday following a six-month investigation. A grand jury indicted him Friday on felony charges of child pornography production and misdemeanor counts of second-degree assault. An investigation continues, and more charges could be filed, the sheriff's office said.
He was removed from his jobs as an instructional assistant at Benjamin Stoddert Middle School in Waldorf and an indoor track coach at nearby La Plata High School late last year when the probe began, Richardson said.
Some of the boys have been tested for HIV, and others are expected to be tested soon, Richardson said. Police are so far not aware of any tests that have come back positive.
The investigation started in December when detectives received a tip about "possible inappropriate behavior with a student while he was coaching track," the sheriff's office said in a statement.
"A student's parent observed suspicious text messages on their child's phone that were sexual in nature," Charles County Sheriff Troy Berry said at a news conference Monday.
Investigators sent Bell's electronic devices from work and from home to the Maryland State Police crime lab, which recovered sexually explicit images involving the boys, Richardson said.
"Some of the evidence ... included graphic images of Bell sexually assaulting victims. Some of the crimes appeared to have been committed on school property, and others at his home in Waldorf," Berry said.
Bell told investigators he is HIV positive, and investigators found evidence corroborating the diagnosis, the sheriff's office said.
CNN's attempts to reach an attorney for Bell weren't immediately successful. The county public defender's office said it wasn't representing him; online court records did not list a lawyer for him.
Bell was being held Monday without opportunity for bail.
The allegations are horrifying, Charles County schools Superintendent Kimberly A. Hill said Monday.
"To our parents and our community who put their faith and trust in us to safeguard our children, I apologize on behalf of Charles County Public Schools," Hill said. "Student safety is job one, and clearly we have work to do to ensure that this will never happen again."
Bell began working for the school system in 2014. He was as an instructional assistant at Waldorf's JP Ryon Elementary School from September 2014 to March 2015, when he took the same position at Stoddert Middle.
He was indoor track coach at Maurice J. McDonough High School in Pomfret during the 2015-16 school year before starting the same post at La Plata High in November, Hill said.
"Mr. Bell has not worked in any of our school buildings since December 22, 2016," Hill said.
Hill sent a message Wednesday to school district staff members and parents pledging full cooperation with investigators as well as support and counseling for the children who were allegedly assaulted. The district also will review its safety protocols.
Waldorf is about 25 miles southeast of Washington.