Usually after a horrendous shooting, the conventional wisdom on what’s “really” to blame has congealed 24 hours later. Not this time. Alexis didn’t use an “assault weapon,” as you already know if you read Ed’s post. He used a shotgun, the weapon of choice of the vice president of the United States. He was, apparently, seriously mentally ill — paranoia, sleep disorder, hearing voices — but had been treated since at least last month and hadn’t (yet?) had his Navy security clearance revoked on grounds of mental unfitness. Time magazine published a mini-bombshell last night about a Pentagon IG report that accused the Navy Yard of cutting corners on screening contractors who might pose a security risk (52 convicted felons received routine access), but as far as I know Alexis has never been convicted of a felony. On the contrary, his boss told Reuters that Alexis passed a background check in July after the firm re-hired him and that he had a “secret clearance” and a common access card for the Navy Yard. Presumably that explains how he got into the otherwise highly secure Naval Sea Systems Command building, which houses lots of classified information. Simply put, he had a right to be there.

Here’s the closest thing I’ve seen to an obvious red flag, but even this has problems:

The former Navy reservist identified by authorities as the gunman in the massacre at the Washington Navy Yard was cited at least eight times during his Navy career for misconduct, officials said Tuesday, including insubordination, disorderly conduct and multiple excessive absences from work.

The Navy also gave Aaron Alexis, 34, an administrative sanction after he was arrested by civilian authorities in DeKalb County, Ga., in 2008 and held for two nights in jail, a Navy official said…

The Navy on Tuesday corrected its initial account of the circumstances under which Alexis left the service. He received an honorable discharge, effective Jan. 31, 2011, a Navy official said. On Monday, the Navy mistakenly said that Alexis had received a general discharge, a less-desirable category that would have indicated to future employers that there was something amiss with his performance.

The official clarified that the service had originally sought to kick out Alexis with a general discharge because of his pattern of misconduct while in uniform, in addition to his arrest by Texas authorities in 2010 for shooting a gun into his neighbor’s apartment. But those proceedings were moving slowly, and it was unclear whether the Navy had sufficient cause to approve a general discharge, the official said.

They knew he was trouble, but not so much trouble that they were prepared to discharge him dishonorably and not even so much that they’d refuse him an honorable discharge on principle. Hard to tell given the paucity of detail here, but it sounds like the misconduct itself in each case was minor; it was the accumulation of incidents, perhaps, not the alarms raised by the severity of any one of them, that forced him out.

As for his motive, to the extent that someone who’s been hearing voices might have a coherent motive, the feds haven’t found one yet. The usual suspicions when a military base is attacked don’t seem to apply: As noted last night, this guy was apparently a fairly devout Buddhist, not a homegrown jihadi like Nidal Hasan, and his best friend and roommate says he doesn’t know of any grudge Alexis might have had against the government. The closest thing to a grievance that the roommate’s aware of was Alexis grumbling a bit after he got back from an assignment from his employer in Japan because he felt he hadn’t been paid the right amount. In fact, the roommate’s leading theory of what drove him over the edge was, uh, violent video games, the default scapegoat when all others have failed. So look forward to an especially stupid debate about that in select media outlets this week.

The best the feds seem able to do right now on motive comes from NBC:

After having been discharged from the Navy, Alexis served as a naval reservist and had been working as a civilian contractor for a division of Hewlett-Packard that was upgrading equipment used on the Navy/Marine Corps intranet, the company confirmed Monday. Investigators said he may have recently lost that job, giving him a grudge to nurse.

Under a new support contract, all HP hardware at the Navy Yard was relocated to Denver last month — leaving few if any support jobs needed in Washington. It wasn’t known whether Alexis’ job was one that was moved to Colorado — and if so, whether he declined to move or was let go as part of the reorganization. HP wouldn’t say Monday whether Alexis was still on its payroll.

Interesting, but that completely contradicts what Alexis’s boss told Reuters. He said that the HP division had just re-hired Alexis in July after he had left the firm in January following the Japan job, and it sounds like he was indeed assigned to work the Navy Yard, not Colorado. Which leaves us stuck at square one.

Exit question: According to NBC, “a shotgun used in the shootings was bought at a Virginia gun store within the last few weeks.” Alexis, as noted above, was being treated for severe mental illness since last month, at least. How was a guy in that condition nonetheless able to purchase a shotgun? Like Jonah Goldberg says, gun-control fans would have an easier time of it if they focused on dangerous gun owners rather than “dangerous guns.”

Update: WaPo updates with more detail on Alexis’s military misconduct: “Aaron Alexis was cited at least eight times for misconduct for offenses as minor as a traffic ticket and showing up late for work but also as serious as insubordination and disorderly conduct, according to a Navy official who spoke on condition of anonymity to discuss the gunman’s personnel record.” He received administrative punishments three times, but not a single court-martial.