I blogged about this last month, remember? At the time, the only evidence was a few YouTube videos of people on gurneys, wheezing. Seemed hard to believe that Assad would shatter the taboo against using WMD for an attack so small-scale as to leave some doubt that WMDs were actually used. And yet here we are.

The slow news cycle is over:

The consul general’s report followed a series of interviews with activists, doctors, and defectors, in what the administration official said was one of the most comprehensive efforts the U.S. government has made to investigate claims by internal Syrian sources. The investigation included a meeting between the consulate staff and Mustafa al-Sheikh, a high-level defector who once was a major general in Assad’s army and key official in the Syrian military’s WMD program.

An Obama administration official who reviewed the document, which was classified at the “secret” level, detailed its contents to The Cable. “We can’t definitely say 100 percent, but Syrian contacts made a compelling case that Agent 15 was used in Homs on Dec. 23,” the official said…

Many believe that Assad is testing U.S. red lines…

“The use of chemical weapons is and would be totally unacceptable,” Obama said Dec. 3, directing his comments at Assad. “If you make the tragic mistake of using these weapons, there will be consequences and you will be held accountable.” That same day, Secretary of State Hillary Clinton added: “we are certainly planning to take action if that eventuality were to occur.”

Follow the link up top for a description of the victims’ symptoms. More than 100 people were allegedly stricken with respiratory problems; five of them died from choking on their own bronchial secretions. The day after it happened, the Syrian American Medical Society spoke to some of the victims and released a report identifying the likely culprit as, indeed, Agent 15:

The Gas effects started [a] few seconds after the area was shelled. Right after the shelling, patients described seeing white gas with odor, then they had severe shortness of breath, loss of vision, inability to speak, flushed face, dizziness, paralysis, nausea and vomiting, and increased respiratory secretions. Doctors who treated patients said that patients had pinpoint pupils and bronchospasm. Patients were treated in a field hospital. Gas masks were not available.

Agent 15 is designed to be incapacitating, not lethal a la sarin, but obviously if the respiratory reaction is dire enough it can be fatal. One question, then: Why? What does Assad gain by “testing U.S. red lines”? Under normal circumstances, defying the United States is wonderful for a fascist’s Middle Eastern street cred, but we’re two years and many thousands of Syrian dead past that. The Sunnis want him gone; the Islamist Sunnis really want him gone. Maybe he’s trying to bait the U.S. into attacking him in order to further solidify his support among Syria’s Alawites? But the Alawites are already entirely committed him, not least because they fear being ethnically cleansed by Sunni rebels if/when they’re overrun. (There are already anecdotal reports of open sectarian warfare at the village level.) The only way using chemical weapons “makes sense” to me is if Assad thought the end was near and wanted to go out in a blaze of insane nihilism by unleashing WMD all over the country. A limited, strategic attack to “test” the U.S. makes no sense, especially since it’s likely to cost him whatever support he still retains from his Russian patrons. Makes me wonder whether this was really a decision by Assad himself or if command and control in the Syrian army has deteriorated to the point that a local commander decided to use Agent 15 on his own initiative. Which, potentially, makes containing the country’s WMDs much more difficult.

The other big question is who in the administration leaked the results of the investigation to The Cable. This has huge consequences for U.S. foreign policy, needless to say; Obama will now be under intense pressure to enforce his “red lines.” Either some pro-interventionist official really screwed him here or this is some sort of deliberate leak to put international pressure on Russia to finally abandon Assad completely. Stay tuned. Exit question: Coming soon — dirty bombs?

Update: Danger Room doesn’t understand why Assad would use Agent 15 either:

Agent 15 is another name for 3-quinuclidinyl benzillate or BZ, a powerful hallucinogen that the American military tested out on its own soldiers during the Cold War. Its emergence on the Syrian battlefield would be nothing short of bizarre. While Syria is well-known to have a massive supply of chemical weapons, international observers haven’t ordinarily included BZ on that list. And while there have been rumors of BZ being used on a battlefield — including one that Iraqi insurgents were dosing themselves with the drug to pump up their aggressiveness — this would be the first confirmed case of BZ employed as a weapon.

Either he really is very gingerly testing U.S. “red lines,” which I don’t understand; or he’s running low on more lethal nerve agents, which no one has suggested; or maybe I’m right that this was a freelance decision by a military commander and Agent 15 was easier for him to get hold of than sarin or VX would be.