CBS Baltimore reports
A call came in at about 2 p.m. for a report of an active shooter situation in the basement of building 19 at Walter Reed. After an investigation by NSA Bethesda, no active shooter was found.
Investigators found that this was a “false alarm and not part of a scheduled drill,” as was reported by the U.S. Navy and other military officials.
The U.S. Navy tweeted later in the evening that the incident was the result of “the improper use of a mass notification system by a tenant command aboard the installation.
They continued to say that while preparing for an upcoming drill, the notification system was “inadvertently enacted without containing the words “EXERCISE” or “DRILL”