The EPA and Clark County School officials now admit the mercury may have been in the building longer than first reported.
Officials say mercury is the cause of the soft lockdown. Students were not allowed to leave or enter the building. At least 6 or 7 students were exposed.
Parents say they were left in the dark as their kids were stuck inside Walter Johnson Junior High School during a mercury contamination scare Wednesday.
Attendance was high after school has been canceled for nearly a week.