For those into pernicious detail, the full FAA rule on airport and aircraft security with comments by various airlines, ALPA, etc., can be found at:
<a href="http://frwebgate5.access.gpo.gov/cgi-bin/waisgate.cgi?WAISdocID=27672016176+0+0+0&WAISaction=retrieve " target="_blank">http://frwebgate5.access.gpo.gov/cgi-bin/waisgate.cgi?WAISdocID=27672016176+0+0+0&WAISaction=retrieve </a>
TR4A's list appears to be self-constructed. It omits a number of agencies with LEOs and includes agencies which would ordinarily be subsumed by a larger department (ministry).
A few other comments:
Bureau of Printing and Engraving (within Treasury, prints currency and stamps. The list excludes the US Mint, which makes coins.)
Defense Nuclear Agency (no agency by that name currently exists)
Dept of Agriculture (Poultry Inspectors, etc. Actually most USDA LEOs are more likely to be Animal, Plant, Health Inspection Service officers who are on duty at airports and ports.)
Dept of Education (the only armed officials of this and a number of other departments MIGHT be Inspectors General staff; i.e., auditors. Hard to believe why these staff feel a need to be armed.)
CIA (I doubt there are many CIA officers flying armed as they would not wish to identify themselves as CIA agents.)
Smithsonian Institution (there are armed guards at the Smithsonian Museums. However, perhaps the more prominent cultural police force is the National Zoological Park Police.
As an example of armed Federal law enforcement agencies omitted from the list, and a great example of the jurisdictional patchwork of law enforcement within Washington DC, there are within 1000 meters of the US Capitol, the following police forces with primary patrol, arrest, etc. jurisdiction for particular areas within that radius:
US Capitol Police
Supreme Court Police
Library of Congress Police
AMTRAK Police (railroad terminal)
US Park Police (Dept. of the Interior)
National Gallery of Art Guards
Smithsonian Guards
Postal Inspectors (post office is nearby)
Federal Protective Service (guards for Federal agency buildings)
Executive Protective Service (for neaerby embassies and consulates)
and the municipal District of Columbia police force. I think the approximate ratio of residents to police in the District of Columbia is >100:1.
Only in America.