Rhode Island Department of Corrections

A third letter allegedly threatening the lives of three correctional officers has surfaced at the medium security prison in Cranston. The discovery prompted a lockdown on Wednesday as authorities searched the John J. Moran Medium Security Facility.

As of 5 p.m. prisoners remained confined to their cells and certain areas, and all personal visits were suspended. Rhode Island Department of Corrections spokesman Cory Cloud said State Police are involved in the investigation.

Update 12/18: Federal prosecutors are suing a Harvard student for causing the false alarm Monday, that led to an extensive search for explosives. They allege Eldo Kim sent emails to campus police and Harvard officials threatening that bombs would go off in buildings on Harvard Yard. According to prosecutors, Kim was trying to get out of taking an exam scheduled for Monday.