A convicted sex offender is back in jail, accused of raping two high school students with special needs.

Earlier this month, two students, ages 17 and 18, told school administrators that a man forced them to perform sexual acts, threatening to hurt them. The two teenagers, who attend special needs classes, picked Matthew Brandon Hall, 28, of Harriman out of a photo lineup, according to the arrest warrant.

Deputies said they’re investigating whether the boys were raped at knife point over a two-to-three year period, according to Roane County Sheriff Jack Stockton. One of the teens told officials that the most recent incident happened the weekend of Jan. 18.

Officials said the alleged rapes did not happen on school property.

On Thursday, Jan. 22, investigators interviewed Hall, where he indicated that he wanted an attorney. The following day, authorities arrested and charged Hall for two counts of rape.

According to the Tennessee Bureau of Investigation’s sex offender registry, Hall was convicted of sexual battery by an authority figure in June 2006.

Hall is classified as violent on the sex offender registry.