We will never know definitively what happened in Benghazi on the night of September 11, 2012. There were too many people involved, too many motivations for the attack, too many conflicting stories after the attack, and too little indisputable evidence about the exact course of events. Add to that the usual fog-of-war issues and you simply have to accept that we’ll never know with absolute certainty everything that happened.

That said, after more than a year of investigation we know a lot. And while I was out of town, David Kirkpatrick of the New York Times produced a state-of-the-art summary of where the best evidence leads us. The whole piece is well worth reading, but I’d highlight a couple of things.

First, Kirkpatrick concludes that the attack was primarily the work of Mr. Abu Khattala, who headed up a local militia that was allied with Ansar al-Sharia, another local militia:

The C.I.A. kept its closest watch on people who had known ties to terrorist networks abroad, especially those connected to Al Qaeda. Intelligence briefings for diplomats often mentioned Sufian bin Qumu, a former driver for a company run by Bin Laden….“We heard a lot about Sufian bin Qumu,” said one American diplomat in Libya at the time. “I don’t know if we ever heard anything about Ansar al-Shariah.” ….The only intelligence connecting Al Qaeda to the attack was an intercepted phone call that night from a participant in the first wave of the attack….But when the friend heard the attacker’s boasts, he sounded astonished, the officials said, suggesting he had no prior knowledge of the assault. ….Three weeks after the attack, on Oct. 3, 2012, leaders of the group’s regional affiliate, Al Qaeda in the Islamic Maghreb, sent a letter to a lieutenant about efforts to crack the new territory….The letter, left behind when the group’s leaders fled French troops in Mali, was later obtained and released by The Associated Press. It tallied up the “spectacular” acts of terrorism the group had accomplished around the region, but it made no mention of Benghazi or any other attacks in Libya.

It’s important to understand exactly what Kirkpatrick is saying: not just that Al Qaeda had essentially nothing to do with the attack in Benghazi, but that our preoccupation with al-Qaeda actively crippled our understanding of what was happening in Libya. And the same thing happened after the attack. Based on the thinnest imaginable pretexts, conservatives have continued to insist that Al Qaeda was responsible, and that’s crippled our ability to understand what really happened that night.

Beyond that, I think Blake Hounshell makes the most salient point: it’s all but impossible to pinpoint exactly what “Al Qaeda” is these days anyway. In reality, there’s a continuum of groups, starting with purely local militants on one end and Al Qaeda central on the other. In between are groups “allied” with Al Qaeda; groups with “ties” to Al Qaeda; groups with members who once worked with Al Qaeda; and groups that have no real connection to Al Qaeda but have similar goals. Trying to figure out which of these groups are “really” Al Qaeda and which aren’t is a mug’s game.

The second point I’d highlight is the role of the infamous “Innocence of Muslims” video. Here is Kirkpatrick:

On Sept. 8, a popular Islamist preacher lit the fuse by screening a clip of the video on the ultraconservative Egyptian satellite channel El Nas….Islamists in Benghazi were watching….By Sept. 9, a popular eastern Libyan Facebook page had denounced the film. On the morning of Sept. 11, even some secular political activists were posting calls online for a protest that Friday, three days away….Around dusk, the Pan-Arab satellite networks began broadcasting footage of protesters breaching the walls of the American Embassy in Cairo, pulling down the American flag and running up the black banner of militant Islam. Young men around Benghazi began calling one another with the news, several said, and many learned of the video for the first time. ….There is no doubt that anger over the video motivated many attackers. A Libyan journalist working for The New York Times was blocked from entering by the sentries outside, and he learned of the film from the fighters who stopped him. Other Libyan witnesses, too, said they received lectures from the attackers about the evil of the film and the virtue of defending the prophet.

If Kirkpatrick sounds slightly exasperated in this passage, it’s because he reported all this more than a year ago. And he wasn’t the only one. For some reason, though, it’s been almost universally shoved down the memory hole. It’s conventional wisdom these days that the video played no role.

But that’s almost certainly not the case. The best evidence suggests that Benghazi was an opportunistic attack: There were lots of militant groups in Benghazi itching for action and looking around for a suitable provocation. Plenty of things might have done the job, and in the end, “Innocence of Muslims” turned out to be one of them.

Not the only one, though. Like it or not, there’s no simple motivation for Benghazi. Likewise, there’s no simple account of how well planned the attack was. Most likely, as Kirkpatrick says, it was neither spontaneous nor the result of long planning. It was something in between, probably in the works for a day or so before it started.

At this point, this is what we know. Benghazi was an opportunistic attack. Several groups were involved, all of them essentially local and with nothing but the most tenuous connections to Al Qaeda. These groups had multiple motivations for the attack, and anger over the “Innocence of Muslims” video was one of them. It provided the spark, and within a day or two it had fanned the flames of resentment enough to make an attack feasible. A few hours later, the attack was planned and then carried out.

That’s the nickel summary. But do read the whole thing to get the full story. For now, it’s about the best, most fair-minded account that we have.