Saturday's chemical weapons attack on the residents of Douma, a suburb of Damascus, Syria, has killed about 100 people.

But who did it?

As a friend asked me via email, "It seems stupid for Assad to have done this, which will force Trump to act. Is it coincidence that this happened so soon after Trump said he wanted to get out of Syria? Could a group that wants us to stay have done this to frame [Bashar] Assad?"

These are good and necessary questions.

Nevertheless, for a number of reasons, it is almost certain that Assad is culpable here.

First off, U.S. military and intelligence monitoring of Assad air forces and chemical weapons related-units is extensive and intensive. This gives context to President Trump's tweet on Sunday morning, blaming Assad.

Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price... — Donald J. Trump (@realDonaldTrump) April 8, 2018



But note that Trump also references the compression zone that the Syrian army has established around Douma.

That the president, not known for his love of small details, knows this indicates that he was told as much in an intelligence briefing. The president's blaming of Assad and Putin also strongly suggests a high intelligence confidence assessment that Assad is culpable.

The speed of this U.S. assessment so quickly after the attack also suggests that the U.S. either tracked the ground forces or Syrian helicopters/jets that launched the weapons against Douma. And there are a number of possible locations from which Assad could have launched this strike. As my map below shows, Assad has many air bases proximate to Douma.





That said, the strongest evidence of Assad's culpability is that his is the only military force in Syria with the capability to carry out this attack.

The victims of this attack show symptoms indicative of a high-concentration Chlorine agent, and no other group in Syria possesses either the means of delivery or concentrated form of Chlorine we see here. Moreover, the rapid death toll from this attack also suggests a nerve agent such as Sarin may have been used.

Still, Assad's near-certain responsibility isn't simply because of his unique chemical weapons capabilities.

It's also the fact that the area surrounding Douma is controlled entirely by Assad regime forces. Even if rebels had somehow attained these weapons from an Assad storage depot, how would they have gotten chemical weapons into a position to fire on Douma?

There's also the question of strategic intent.

While it might seem plausible, and the Russians will almost certainly claim it, that rebels would use chemical weapons (weapons they don't have) to kill their own people and thus compel the Trump administration to change its mind about withdrawing, the rebels are not stupid. They know that the U.S. would detect their involvement in any such attack and that the U.S. has largely given up on trying to overthrow Assad's regime.

On the flip side (morality aside), Assad has every reason to carry out this attack. After all, Douma is the last stubborn holdout around Damascus and chemical weapons offer a way to flush out rebels and their families hiding below ground while terrorizing others. Putin would also find this funny in that it offers a way to give an ironic one-fingered salute to the West in the context of Russian embarrassment over the Sergei Srkipal nerve agent scandal.

More broadly, aside from a shrinking rebel bubble in Idlib province and a U.S. protected area east of the Euphrates, Assad holds the dominant position in Syria's seven-year civil war.

Finally, Assad has consistently gambled that Trump's 2017 strike on his chemical weapons forces was a one-time thing and that future strikes would be deterred by Russian threats against further U.S. escalation.

I suspect he is wrong.