Again? Nearly two years after Aaron Alexis killed twelve people before getting killed by police, the US Navy has locked down the Washington Navy Yard in DC with an active-shooter warning:

#BREAKING: @NavalDistWashington Navy Yard on lockdown/shelter in place. No incident can be confirmed as of yet. More to follow.

— U.S. Navy (@USNavy) July 2, 2015

ABC News reports that an active shooter hasn’t been confirmed as of yet. Reuters hasn’t confirmed one yet either, but they do note that US law enforcement has been on high alert for potential terrorist activity this weekend anyway. The Washington Post has only scant details at the moment:

U.S. Park Police confirmed that officers responded Thursday to reports of an active shooter at the Washington Navy Yard.

The call came in about 7:40 a.m.

Fox says it has independently confirmed the lockdown, but not the shooter:

.@JenGriffinFNC reports that the Navy Yard spokesman confirms base is on lockdown amid reports of active shooter pic.twitter.com/O1IyFlxtu4

— FOX & friends (@foxandfriends) July 2, 2015

We’ll have more as this develops. Everything at the moment is precautionary, so don’t assume anything, and especially don’t take initial reports as verified fact. In almost every one of these cases, people end up having to unlearn what they think they know about them.

Update: One of ABC’s sources says the lockdown may have been triggered by a “suspicious person”:

NEW: Defense official says situation at Navy Yard based on report of “suspicious person”; nothing yet confirmed – @LMartinezABC

— ABC News (@ABC) July 2, 2015

As I note above, we don’t even know for sure that shots have been fired yet. The lockdown does follow live-shooter protocol, though.

Update: Fox5 in DC says that multiple sources have confirmed that a shooting took place:

FOX 5’s Assignment Manager Doug Buchanan says multiple sources confirm that there was a shooting at the location just after 7:30 a.m.

Update: This is interesting:

Police have found the person who made the original 911 call and are conducting interviews, according to NBC Washington. They have not found any evidence of a shooting at this time.

NBC’s affiliate in the market reports that other law-enforcement assets are being waved off, perhaps because the Navy Yard has been saturated already.

Update: Starting to see more media orgs reporting that this may have been nothing after all:

UPDATE: Navy Yard spokesman says no casualties, no shooter spotted at Washington Navy Yard – Local CBS Radio

— Reuters (@Reuters) July 2, 2015

Police working to complete sweep at Washington, DC, Navy Yard after security incident; no active threat found, so far, sources tell @ABC.

— ABC News (@ABC) July 2, 2015

If nothing else, it will have made for a good run-through for a real case.

Update: More indications that this may be nothing:

From @krisvancleave DC Police Chief Cathy Lanier tells me via email "nothing found so far" at Navy Yard.

— Mark Knoller (@markknoller) July 2, 2015

A named source makes this a little more solid.

Update: Looks like the all-clear has been given, and it’s nothing … or maybe a different kind of bad (via Twitchy):

"We suspect this was a hoax," officials say after Washington #NavyYard lockdown http://t.co/6JQaHM8ogx pic.twitter.com/LtnojxHrRf

— BBC North America (@BBCNorthAmerica) July 2, 2015