It was a drug investigation at Clover High School that led York County deputies to 17-year-old Alex Littlejohn, who allegedly had a stash of prescription drugs in his book bag.

There is more to Alex Littlejohn's past that many of his teachers and classmates did not know.

He is a registered sex offender who had pleaded guilty to attacking a 12-year-old girl in north Charlotte in July 2012.

"I did snap that night and I actually could've hurt someone. I know I could've. I was very, very angry for a long time and I still am," the girl's mother told Eyewitness News.

She said that Littlejohn was one of three teenagers who lured her daughter into a vacant house and sexually assaulted her.

In September, Littlejohn pleaded guilty to sexual battery, a misdemeanor, and had to register as a sex offender.

His family moved, and he transferred to Clover High School, where he told them about his past.

"We were aware that he was on the sex offender registration list," said the schools' spokesman Mychal Frost.

Frost said that only a handful of people at the school -- administrators, the resource officer and Littlejohn's probation officer -- knew about his status and they kept a close eye on him.

They also decided early on not to move him to the alternative school program because it includes younger students, some of them as young as the victim of his assault.

"We felt it was in the best interest of everyone to keep him in his high school environment where he would be in a position with students of his own age," Frost said.

Teachers and students at Clover High School may have had no idea that one of their classmates was a sex offender, and some parents said that makes them nervous.

"That is scary. There are a lot of predators out there now," said Jeannine Wyatt.

Littlejohn's case raises the question of whether other schools have students who are also registered sex offenders. The top man at Charlotte Mecklenburg Schools said not here.

"To our knowledge we have no students who are on any official sex offender registration," Dr. Heath Morrison said Wednesday.

Morrison said they would find out about any sex offenders when students register, and also from the court system or probation officers.

If a student does enroll, Morrison said someone would be watching them very closely.

"That student would be assigned a one on one SRO who would touch base with them every day," Dr. Morrison said.

The mother of the 12-year-old who was attacked last summer said she would like to see a law that would keep sex offenders out of the main population of schools.

"If I had justice the way I wanted justice, these young men would not be attending school, they would not be around other children," she said.

One of the other two teenagers who allegedly attacked her daughter is still waiting for trial. The third is a juvenile and his court records are not public record.