Why they decided to put this out, I don’t know. I suppose they decided that the public has a right to know, although nothing much happens in the video; the right to know naturally doesn’t extend to the mayhem itself, just the prelude. But the impending doom that remains will make your blood run cold regardless. It’s one thing to know that it was an ambush from reading about it in the newspaper, it’s another thing to watch this lunatic creep towards unsuspecting people milling about in the hall, shotgun in hand. Dreadful, in every sense.

Incidentally, the feds think they’ve figured out why Alexis’s arrest record didn’t set off enough alarms to have his security clearance revoked. He apparently lied about his past, and when the background checkers inquired with local police for details, they were … refused.

A central focus of the review is a 2007 background check of Mr. Alexis conducted by US Investigations Services LLC, a Falls Church, Va., company facing a criminal investigation over allegations that it rushed cases through the clearance process without proper review.

Last week, the Office of Personnel Management, the agency in charge of overseeing most federal background security checks, said USIS had conducted a complete investigation of Mr. Alexis, including information on the 2004 arrest.

On Monday, the agency said Mr. Alexis had turned in an incomplete security background form in 2007 that omitted information about the arrest as well as financial problems in his past. After uncovering the problems in the normal course of the examination, investigators asked the Seattle Police Department for information on Mr. Alexis. But the department refused, according to the OPM…

“Had the Seattle Police Department permitted OPM to obtain the law-enforcement records, it is possible that additional information may have been obtained,” according to an agency official. “However, OPM cannot compel police departments to cooperate.”

The feds have a bunch of his thumb drives and computers and, while they’re not revealing the contents, they say they now have reason to believe that Alexis thought his mind was being controlled by extremely low frequency electromagnetic waves. That presumably explains the cryptic “my ELF weapon” inscription on his shotgun. (There were other inscriptions too, including “End to the torment!” You can see photos on the FBI’s website.) As for the mysterious stand-down order given to the Capitol Police SWAT team, they were still waiting for an explanation from their superiors at last check. Here’s one possibility that occurred to me after last week’s post, though: What if their supervisors feared the Navy Yard shooting was a diversionary tactic? Terrorists have pulled that before, hitting a soft target somewhere to draw away police to the scene and then launching a more fearsome attack on a more valuable target nearby. Could be Capitol PD thought the chaos at the Navy Yard was designed to get SWAT to commit there, with something even more sinister planned for the Capitol itself.