EACH NEW detail that emerges about the alleged sexual abuse of students in Charles County brings an added horror. The number of boys victimized has grown to 24, and it’s feared there are more. Some of the assaults occurred in the classroom of a middle school where the alleged assailant worked as a teacher’s aide. The victims were not only abused but also allegedly deliberately exposed to HIV.

How such events could have gone undetected for two years is the unsettling question that school and law enforcement officials in this Southern Maryland county must answer.

A 119-count indictment was announced last week against Carlos Deangelo Bell, 30, a former instructional assistant at Benjamin Stoddert Middle School who also coached indoor track at La Plata High School. Among the charges: multiple counts of sexual abuse of a minor, production of child pornography, attempted exposure to HIV. Authorities said Mr. Bell acknowledged he is HIV-positive. Mr. Bell, his attorney told reporters, is looking forward to fighting the allegations.

The alleged crimes span from May 2015 to June 2017. School officials had been told Dec. 22, 2016, that Mr. Bell was under investigation by the sheriff’s special victims unit following a complaint from a parent, and he was immediately removed from the classroom. He was fired in January when he failed to show up for his reassignment to administrative duty, but he wasn’t arrested until June 30. The lag was blamed on a backlog at the state police crime lab that delayed the processing of evidence from his computer and other electronics. It is maddening to think that children may have been victimized while evidence sat in a lab waiting to be analyzed.

“Grieving” is how Schools Superintendent Kimberly A. Hill described the reaction of the school system. A public Web page was established and meetings scheduled to share information with the public, free counseling was arranged for students and their families, and the principal of Stoddert was reassigned. Most importantly, the system has undertaken a review of security protocols and sexual abuse training. “What could we have done? What should we do?” are the questions, Ms. Hill told us, that officials are grappling with. As troubling as it would be to discover there were things missed or done inappropriately by school personnel, even more unsettling is the prospect of predators so adept at deception that they are able to fool not only the children they victimize but also the adults who are supposed to protect them.