Arkansas ? A teenager who helped shoot and kill five people during a school yard rampage at his middle school reached his 21st birthday Thursday and was expected to walk out of a federal detention center.

Federal authorities would not confirm Mitchell Johnson’s release, saying privacy laws prevented them from commenting because Johnson was a minor when he and another boy gunned down four classmates and a teacher behind Jonesboro Westside Middle School.

Because of a since-closed loophole in Arkansas’ juvenile justice system, the state had no way to hold Johnson and Andrew Golden beyond their 18th birthdays. Federal prosecutors used weapons laws to keep the boys locked up until age 21.

State Rep. Dustin McDaniel, who represents the northeastern Arkansas town, said Thursday that Johnson’s expected release was a painful reminder of the violence.