Montgomery County police block the entrance of the Walter Reed National Military Medical Center on Nov. 27, in what proved to be an errant active-shooter alert that took an hour to call off. (Jose Luis Magana/AP)

The errant “active shooter” alerts that placed the Walter Reed National Military Medical Center on lockdown last month appear to have resulted from multiple miscommunications at the military complex in Bethesda, Md., that houses the prestigious health facility, according to accounts from an installation spokesman.

As the confusion unfolded, swarms of tactical officers searched for a gunman who didn’t exist while hospital staff members were told to move patients to secure rooms, lock doors and turn off lights. The lockdown lasted approximately 80 minutes.

But two weeks after the Nov. 27 incident, a detailed accounting still is not available, according to Jeremy Brooks, a spokesman for Naval Support Activity Bethesda, the entity that helps run the installation, about two miles north of Washington, and that hosts other tenants besides Walter Reed.

The investigation so far suggests that the panic built after a person at one facility at the installation inadvertently sent an alert about an active shooter, realized the error, and “immediately attempted but failed to recall the information,” Brooks said.

He said the person who sent the first alert and tried to recall it appears to have waited about an hour to call security at the installation to say the alert wasn’t for a real shooter.

It was not clear whether the original alert, which was not planned and should not have gone out regardless, contained the word “drill” or “exercise,” Brooks said, but it set off a chain of responses and follow-up alerts by others on the campus that did not include any such caution.

The original faulty alert was quickly disseminated at the installation by text, email and automated phone calls, Brooks said.

A person at Walter Reed who listened to an automated call was led to believe that it was a genuine alert about a shooter, either because there was no disclaimer or the person listening didn’t hear it, Brooks said.

Information from the person listening to the call was then relayed to a dispatch center and from there to security officials on the installation, who by then had reason to believe that the report of an active shooter was real and sent out an alert, Brooks said Monday. That alert was apparently seen by emergency staffers at Walter Reed.

“There is currently an active shooter on the compound,” the Walter Reed alert said, as confirmed by Brooks. “Move all patients and staff to a secure location, lock all doors, turn off all lights, and remain in [a] secure location until notified by security.”

Brooks declined to say why the original messenger waited an hour to call security or whether disciplinary actions have been taken. He also declined to identify the person or where the person works, citing the ongoing investigation.

The probe has not uncovered ill intent or bad actors. “It was human error,” Brooks said.

Brooks also declined to discuss what kind of verification systems, if any, were in place for such alerts or what capability security officers had to quickly track down who sent the erroneous alert.

“At the end of the investigation, weaknesses will be examined, and lessons learned will be applied to how we handle future exercises and real-world events,” Brooks said.

There is no fixed completion date for the investigation, he said.

The alerts sent fear rippling across the installation on the outskirts of Washington. Anxiety then spread around the country as family members of employees and visitors to the sprawling campus heard about the threat through texts from loved ones, or began following what erupted as a nationwide, breaking-news story.

Also responding en masse as they pulled away from their regular policing duties were teams of officers from Montgomery County, the jurisdiction that surrounds the installation. Late-afternoon commuters sat snarled in traffic.

The facility, about two miles north of Washington, is best known for the Walter Reed National Military Medical Center, which is home to the institutions formerly known as the Walter Reed Army Medical Center and the National Naval Medical Center. The facility cares for active-duty service members and their family members, and is charged with providing care to the president, members of Congress and other government officials.

Walter Reed operates out of a larger, gated military installation that includes the Naval Medical Research Center, the Uniformed Services University of the Health Sciences and the Naval Bloodborne Infection Management Center among its tenants.

Word of the alert last month also spread within the various organizations at the site, eventually leading to calls to 911 in Montgomery County. Police there called NSA Bethesda security staffers, who said they were investigating the incident, prompting Montgomery police officials to decide to send help.