ISTANBUL, Turkey—Days ago, in Ankara, U.S. Secretary of State Rex Tillerson signaled that the U.S. had no quarrel with Syrian dictator Bashar al-Assad, a man Tillerson’s predecessor compared to Adolf Hitler after he slaughtered more than 1,000 people with poison gas in 2013.

The “longer-term status of President Assad,” Tillerson said, “will be decided by the Syrian people,” a euphemism used by Damascus, Moscow, and Tehran to indicate that he isn’t going anywhere.

White House press secretary Sean Spicer used almost identical language the next day, saying, “Well, I think with respect to Assad, there is a political reality that we have to accept in terms of where we are right now.”

But the gas, it appears, is raining down once again on civilians.

In a video made Tuesday, Dr. Shajul Islam showed the camera a young man lying on a gurney with a catatonic expression on his face. His pupils were shrunk to the size of pinheads. “This is not chlorine,” he said. “We do not smell chlorine on this patient.” The industrial chemical has often been used as crude weapon on the Syrian battlefield.

Perhaps this time it was organic phosphate, another easily acquired chemical.

But other Syrians—and outside observers—say that it’s more likely the Assad regime dropped sarin gas on civilians—a much more sophisticated odorless and colorless nerve agent that Damascus was supposed to have gotten rid of as part of a U.S.-Russian-brokered deal in 2013.

“If it’s what it looks like, it’s clearly a war crime,” said a senior State Department official, speaking to reporters on condition of anonymity.

"It has the fingerprints of a regime attack," added a U.S. intelligence official. "If the Assad regime was indeed responsible for perpetrating the attack, the reported casualties figures would make it the biggest incident like this since the Syrian regime's August 2013 sarin attack against the Damascus suburbs."

As ever in the six-year civil war, the death toll depends on whom you consult. The London-based Syrian Observatory for Human Rights puts it at 58. The White Helmets, on-the-ground first responders, at first said the figure was closer to 50. Other estimates are upward of 100 dead, with probably about 300 more injured.

The “poisonous gas,” as one Syrian activist put it, was dropped by helicopters in a series of airstrikes in the city of Khan Sheikhoun, Idlib province, one of the last enclaves of rebel control in the area, mainly administered by al Qaeda and other Islamist groups.

But videos on social media do not show jihadis lying as waxy corpses in makeshift hospitals. They show children. In one image, published by Al Jazeera, a half dozen are laid out in a row under a blanket in the back of a pickup truck. Boys on the left, girls on the right, their ages probably as young as 3.

Dr. Firas Jundi, health minister for the opposition interim government, told The Daily Beast he had the names of 60 people killed in the gas attack. He said the death toll was bound to rise as there are 300 wounded, many in critical care hospitals and clinics throughout the province.

The number of victims was an indication that this is not chlorine gas, he added in a Whatsapp conversation from Idlib, where the interim government is located. "Usually chlorine doesn't kill such big number.”

He said the signs of trauma suggested a nerve agent like sarin was used in the attack, but testing was needed to say for sure. He said local authorities have recovered parts of the rocket that carried the gas canisters and are ready to turn them over to international investigators.

“What I noticed about the victims was they had difficulty breathing, many had lost consciousness and the pupils of their eyes had narrowed,” he said.

“If there are pinpoint pupils and convulsions, it’s likely nerve gas. The number of deaths is too high for chlorine for an outdoor attack,” said Andy Weber, former assistant secretary of defense for nuclear, chemical, and biological defense programs under the Obama administration.

“Pinpoint pupils is diagnostic for sarin,” said Ambassador Laura Holgate, who was the Obama White House’s senior director for weapons of mass destruction. “Sarin kills you with a drop on your skin,” though its lethality depends on how its delivered, and the weather conditions when its dispersed.

“There was never any indication that we didn’t get all the sarin in the 2014 elimination project,” said Holgate, who was part of the team that negotiated the disarming Syria of its chemical arms in 2014, together with Moscow. “If he has sarin, it wasn’t declared or destroyed as it should have been,” as part of the Organization for the Prohibition of Chemical Weapons-monitored operation.

“We may have gotten all of it, but they may have made more,” said Weber, who was part of the same Obama administration disarmament mission. “It’s a chemical synthesis process they obviously know how to do. Their entire [chemical warfare] program was indigenous.”

“You don’t have to have tons of it to deliver a few small bombs,” he added.

The only way to know definitively what was used is for the OPCW to gather its own tissue samples from survivors, which is difficult to do in hot zones that are still under fire. Otherwise, both former officials said, you have “chain of custody” issues in that you are trusting a human-rights group or other a local militia group’s account on exactly where and when a sample was taken.

“You’re taking their word for where they got it,” she said. “That’s why the U.S. government was always leery to lend its credence to the claims.”

Nevertheless, there are early and strong indicators of the Idlib attack’s perpetrator. “The fact that it was air delivered means it was definitely the regime that did it,” said Weber, who is now senior fellow at the Belfer Center.

The airstrikes started at around 6:30 Tuesday morning.

A hospital treating patients of the alleged chemical attack was also bombed, according to AFP, which was reporting from the location.

This was not the only attack on civilians Tuesday. “The people in Idlib are terrified,” Jundi said. A hospital was bombed in Salqin, killing 15 people, he said. “Everyone here is waiting for death.”

Othman Al Khani, a Khan Sheikhoun resident who lives about one mile from the area targeted, said it was residential, and there were no military installations or personnel stationed there. At least half the residents were internally displaced families from Hama province.

“Last night was very long and tiring for the people of Khan Sheikhoun,” he told The Daily Beast. “We were under bombardment until late at night, and then when people slept they slept very deeply. That is why when the gas started to leak into the houses people didn't notice it. They were deep in sleep.”

But Khani was awake and listening to rebel radio warning there was a Sukhoi combat plane flying in the vicinity.

“I heard the sort of small explosion of the type that occurs when a missile doesn’t blow up,” he said. The plane flew another 15 minutes and carried out three more strikes, he said.

The first strike turned out to be the most lethal. The local first responders from the Civil Defense had come ill-equipped and were all affected by the gas, he said.

Later in the day, he witnessed the Khan Sheikhoun hospital and the Civil Defense center coming under attack. “I was there, inside the Civil Defense center,” he said. The Center, like the hospital, is located in a cave area out of the city. “The warplane kept maneuvering above us for half an hour and hit the two places with more than ten strikes,” he said. But they were well protected by big boulders, and only the equipment and cars outside the two locations were destroyed.

Idlib province has become a frequent drop zone for chemical agents. A year-long study conducted jointly by the United Nations and the OPCW found last year that regime helicopters dropped chlorine-filled bombs on the towns of Talmenes and Sarmin, the former in late April 2014, the latter in mid-March 2015.

Chlorine is also a common industrial chemical. Its most familiar use is to keep water clean in swimming pools. But it was also one of the first chemical weapons used in World War I more than a century ago, and it is banned as an agent of warfare by the Chemical Weapons Convention. Syria signed on to that treaty in 2013 as part of a deal to acknowledge and relinquish its stocks of sarin, VX, and mustard gas. The alternative was to be U.S. intervention in the conflict.

The regime had used sarin that year in East Ghouta, a suburb of Damascus, against opposition forces. Around 1,400 people were killed in that attack, according to the U.S. government, in the deadliest chemical weapons use since Iraqi dictator Saddam Hussein’s gassing of Kurds in Halabja in 1988.

Even after the OPCW judged that 99.6 percent of all declared chemicals in Syria had been removed from the country, it still found victims who had been exposed to sarin, a substance that is neither easily handled nor easily weaponized.

Last December, the regime reportedly used sarin again in eastern Hama, a day after Islamic State terror group fighters recaptured the ancient city of Palmyra. More than 90 were killed and 300 were hospitalized.

"I'm appalled by the reports that there's been a chemical weapons attack on a town south of Idlib allegedly by the Syrian regime," British prime minister Theresa May said in a statement.

"If proven, this will be further evidence of the barbarism of the Syrian regime... I'm very clear that there can be no future for Assad in a stable Syria which is representative of all the Syrian people and I call on all the third parties involved to ensure that we have a transition away from Assad," she added, using language that could not have been more different from the Trump administration's earlier statements.

But by Wednesday afternoon, the Trump administration had begun to shift that accommodationist tone, blaming the Assad regime—and President Obama—for the attacks. "These heinous actions by the Bashar al-Assad regime are a consequence of the past administration's weakness and irresolution." Spicer said.

"It is clear that this is how Bashar al-Assad operates: with brutal, unabashed barbarism," Tillerson said in a statement. "Anyone who uses chemical weapons to attack his own people shows a fundamental disregard for human decency and must be held accountable."

"Those who defend and support him, including Russia and Iran, should have no illusions about Assad or his intentions," Tillerson added.

He neglected to mention his own tacit support of Assad, voiced just days ago.