LINCOLN, Neb. (AP) — An envelope filled with cornstarch forced a Nebraska prison to close its entrance for nearly two hours while authorities investigated the suspicious item. Staff members at the Nebraska State Penitentiary in Lincoln flagged the envelope around 11:30 a.m. Thursday because it contained an unknown white powdery substance.

Corrections department spokesman James Foster says crews from Lincoln Fire and Rescue, the Nebraska State Patrol and the city health department arrived at the prison and determined that the substance was cornstarch.

Foster says the prison returned to its normal operations around 1:15 p.m.