Barack Obama did not tell the whole story this autumn when he tried to make the case that Bashar al-Assad was responsible for the chemical weapons attack near Damascus on 21 August. In some instances, he omitted important intelligence, and in others he presented assumptions as facts. Most significant, he failed to acknowledge something known to the US intelligence community: that the Syrian army is not the only party in the country’s civil war with access to sarin, the nerve agent that a UN study concluded – without assessing responsibility – had been used in the rocket attack. In the months before the attack, the American intelligence agencies produced a series of highly classified reports, culminating in a formal Operations Order – a planning document that precedes a ground invasion – citing evidence that the al-Nusra Front, a jihadi group affiliated with al-Qaida, had mastered the mechanics of creating sarin and was capable of manufacturing it in quantity. When the attack occurred al-Nusra should have been a suspect, but the administration cherry-picked intelligence to justify a strike against Assad.

In his nationally televised speech about Syria on 10 September, Obama laid the blame for the nerve gas attack on the rebel-held suburb of Eastern Ghouta firmly on Assad’s government, and made it clear he was prepared to back up his earlier public warnings that any use of chemical weapons would cross a ‘red line’: ‘Assad’s government gassed to death over a thousand people,’ he said. ‘We know the Assad regime was responsible … And that is why, after careful deliberation, I determined that it is in the national security interests of the United States to respond to the Assad regime’s use of chemical weapons through a targeted military strike.’ Obama was going to war to back up a public threat, but he was doing so without knowing for sure who did what in the early morning of 21 August.

He cited a list of what appeared to be hard-won evidence of Assad’s culpability: ‘In the days leading up to August 21st, we know that Assad’s chemical weapons personnel prepared for an attack near an area where they mix sarin gas. They distributed gas masks to their troops. Then they fired rockets from a regime-controlled area into 11 neighbourhoods that the regime has been trying to wipe clear of opposition forces.’ Obama’s certainty was echoed at the time by Denis McDonough, his chief of staff, who told the New York Times: ‘No one with whom I’ve spoken doubts the intelligence’ directly linking Assad and his regime to the sarin attacks.

But in recent interviews with intelligence and military officers and consultants past and present, I found intense concern, and on occasion anger, over what was repeatedly seen as the deliberate manipulation of intelligence. One high-level intelligence officer, in an email to a colleague, called the administration’s assurances of Assad’s responsibility a ‘ruse’. The attack ‘was not the result of the current regime’, he wrote. A former senior intelligence official told me that the Obama administration had altered the available information – in terms of its timing and sequence – to enable the president and his advisers to make intelligence retrieved days after the attack look as if it had been picked up and analysed in real time, as the attack was happening. The distortion, he said, reminded him of the 1964 Gulf of Tonkin incident, when the Johnson administration reversed the sequence of National Security Agency intercepts to justify one of the early bombings of North Vietnam. The same official said there was immense frustration inside the military and intelligence bureaucracy: ‘The guys are throwing their hands in the air and saying, “How can we help this guy” – Obama – “when he and his cronies in the White House make up the intelligence as they go along?”’

The complaints focus on what Washington did not have: any advance warning from the assumed source of the attack. The military intelligence community has for years produced a highly classified early morning intelligence summary, known as the Morning Report, for the secretary of defence and the chairman of the Joint Chiefs of Staff; a copy also goes to the national security adviser and the director of national intelligence. The Morning Report includes no political or economic information, but provides a summary of important military events around the world, with all available intelligence about them. A senior intelligence consultant told me that some time after the attack he reviewed the reports for 20 August through 23 August. For two days – 20 and 21 August – there was no mention of Syria. On 22 August the lead item in the Morning Report dealt with Egypt; a subsequent item discussed an internal change in the command structure of one of the rebel groups in Syria. Nothing was noted about the use of nerve gas in Damascus that day. It was not until 23 August that the use of sarin became a dominant issue, although hundreds of photographs and videos of the massacre had gone viral within hours on YouTube, Facebook and other social media sites. At this point, the administration knew no more than the public.

Obama left Washington early on 21 August for a hectic two-day speaking tour in New York and Pennsylvania; according to the White House press office, he was briefed later that day on the attack, and the growing public and media furore. The lack of any immediate inside intelligence was made clear on 22 August, when Jen Psaki, a spokesperson for the State Department, told reporters: ‘We are unable to conclusively determine [chemical weapons] use. But we are focused every minute of every day since these events happened … on doing everything possible within our power to nail down the facts.’ The administration’s tone had hardened by 27 August, when Jay Carney, Obama’s press secretary, told reporters – without providing any specific information – that any suggestions that the Syrian government was not responsible ‘are as preposterous as suggestions that the attack itself didn’t occur’.

On 29 August, the Washington Post published excerpts from the annual budget for all national intelligence programmes, agency by agency, provided by Snowden. In consultation with the Obama administration, the newspaper chose to publish only a slim portion of the 178-page document, which has a classification higher than top secret, but it summarised and published a section dealing with problem areas. One problem area was the gap in coverage targeting Assad’s office. The document said that the NSA’s worldwide electronic eavesdropping facilities had been ‘able to monitor unencrypted communications among senior military officials at the outset of the civil war there’. But it was ‘a vulnerability that President Bashar al-Assad’s forces apparently later recognised’. In other words, the NSA no longer had access to the conversations of the top military leadership in Syria, which would have included crucial communications from Assad, such as orders for a nerve gas attack. (In its public statements since 21 August, the Obama administration has never claimed to have specific information connecting Assad himself to the attack.)

The Post report also provided the first indication of a secret sensor system inside Syria, designed to provide early warning of any change in status of the regime’s chemical weapons arsenal. The sensors are monitored by the National Reconnaissance Office, the agency that controls all US intelligence satellites in orbit. According to the Postsummary, the NRO is also assigned ‘to extract data from sensors placed on the ground’ inside Syria. The former senior intelligence official, who had direct knowledge of the programme, told me that NRO sensors have been implanted near all known chemical warfare sites in Syria. They are designed to provide constant monitoring of the movement of chemical warheads stored by the military. But far more important, in terms of early warning, is the sensors’ ability to alert US and Israeli intelligence when warheads are being loaded with sarin. (As a neighbouring country, Israel has always been on the alert for changes in the Syrian chemical arsenal, and works closely with American intelligence on early warnings.) A chemical warhead, once loaded with sarin, has a shelf life of a few days or less – the nerve agent begins eroding the rocket almost immediately: it’s a use-it-or-lose-it mass killer. ‘The Syrian army doesn’t have three days to prepare for a chemical attack,’ the former senior intelligence official told me. ‘We created the sensor system for immediate reaction, like an air raid warning or a fire alarm. You can’t have a warning over three days because everyone involved would be dead. It is either right now or you’re history. You do not spend three days getting ready to fire nerve gas.’ The sensors detected no movement in the months and days before 21 August, the former official said. It is of course possible that sarin had been supplied to the Syrian army by other means, but the lack of warning meant that Washington was unable to monitor the events in Eastern Ghouta as they unfolded.

The sensors had worked in the past, as the Syrian leadership knew all too well. Last December the sensor system picked up signs of what seemed to be sarin production at a chemical weapons depot. It was not immediately clear whether the Syrian army was simulating sarin production as part of an exercise (all militaries constantly carry out such exercises) or actually preparing an attack. At the time, Obama publicly warned Syria that using sarin was ‘totally unacceptable’; a similar message was also passed by diplomatic means. The event was later determined to be part of a series of exercises, according to the former senior intelligence official: ‘If what the sensors saw last December was so important that the president had to call and say, “Knock it off,” why didn’t the president issue the same warning three days before the gas attack in August?’

The NSA would of course monitor Assad’s office around the clock if it could, the former official said. Other communications – from various army units in combat throughout Syria – would be far less important, and not analysed in real time. ‘There are literally thousands of tactical radio frequencies used by field units in Syria for mundane routine communications,’ he said, ‘and it would take a huge number of NSA cryptological technicians to listen in – and the useful return would be zilch.’ But the ‘chatter’ is routinely stored on computers. Once the scale of events on 21 August was understood, the NSA mounted a comprehensive effort to search for any links to the attack, sorting through the full archive of stored communications. A keyword or two would be selected and a filter would be employed to find relevant conversations. ‘What happened here is that the NSA intelligence weenies started with an event – the use of sarin – and reached to find chatter that might relate,’ the former official said. ‘This does not lead to a high confidence assessment, unless you start with high confidence that Bashar Assad ordered it, and began looking for anything that supports that belief.’ The cherry-picking was similar to the process used to justify the Iraq war.

*The White House needed nine days to assemble its case against the Syrian government. On 30 August it invited a select group of Washington journalists (at least one often critical reporter, Jonathan Landay, the national security correspondent for McClatchy Newspapers, was not invited), and handed them a document carefully labelled as a ‘government assessment’, rather than as an assessment by the intelligence community. The document laid out what was essentially a political argument to bolster the administration’s case against the Assad government. It was, however, more specific than Obama would be later, in his speech on 10 September: American intelligence, it stated, knew that Syria had begun ‘preparing chemical munitions’ three days before the attack. In an aggressive speech later that day, John Kerry provided more details. He said that Syria’s ‘chemical weapons personnel were on the ground, in the area, making preparations’ by 18 August. ‘We know that the Syrian regime elements were told to prepare for the attack by putting on gas masks and taking precautions associated with chemical weapons.’ The government assessment and Kerry’s comments made it seem as if the administration had been tracking the sarin attack as it happened. It is this version of events, untrue but unchallenged, that was widely reported at the time.

An unforeseen reaction came in the form of complaints from the Free Syrian Army’s leadership and others about the lack of warning. ‘It’s unbelievable they did nothing to warn people or try to stop the regime before the crime,’ Razan Zaitouneh, an opposition member who lived in one of the towns struck by sarin, told Foreign Policy. The Daily Mail was more blunt: ‘Intelligence report says US officials knew about nerve-gas attack in Syria three days before it killed over 1400 people – including more than 400 children.’ (The number of deaths attributable to the attack varied widely, from at least 1429, as initially claimed by the Obama administration, to many fewer. A Syrian human rights group reported 502 deaths; Médicins sans Frontières put it at 355; and a French report listed 281 known fatalities. The strikingly precise US total was later reported by the Wall Street Journal to have been based not on an actual body count, but on an extrapolation by CIA analysts, who scanned more than a hundred YouTube videos from Eastern Ghouta into a computer system and looked for images of the dead. In other words, it was little more than a guess.)

Five days later, a spokesman for the Office of the Director of National Intelligence responded to the complaints. A statement to the Associated Press said that the intelligence behind the earlier administration assertions was not known at the time of the attack, but recovered only subsequently: ‘Let’s be clear, the United States did not watch, in real time, as this horrible attack took place. The intelligence community was able to gather and analyse information after the fact and determine that elements of the Assad regime had in fact taken steps to prepare prior to using chemical weapons.’ But since the American press corps had their story, the retraction received scant attention. On 31 August the Washington Post, relying on the government assessment, had vividly reported on its front page that American intelligence was able to record ‘each step’ of the Syrian army attack in real time, ‘from the extensive preparations to the launching of rockets to the after-action assessments by Syrian officials’. It did not publish the AP corrective, and the White House maintained control of the narrative.

So when Obama said on 10 September that his administration knew Assad’s chemical weapons personnel had prepared the attack in advance, he was basing the statement not on an intercept caught as it happened, but on communications analysed days after 21 August. The former senior intelligence official explained that the hunt for relevant chatter went back to the exercise detected the previous December, in which, as Obama later said to the public, the Syrian army mobilised chemical weapons personnel and distributed gas masks to its troops. The White House’s government assessment and Obama’s speech were not descriptions of the specific events leading up to the 21 August attack, but an account of the sequence the Syrian military would have followed for any chemical attack. ‘They put together a back story,’ the former official said, ‘and there are lots of different pieces and parts. The template they used was the template that goes back to December.’ It is possible, of course, that Obama was unaware that this account was obtained from an analysis of Syrian army protocol for conducting a gas attack, rather than from direct evidence. Either way he had come to a hasty judgment.

The press would follow suit. The UN report on 16 September confirming the use of sarin was careful to note that its investigators’ access to the attack sites, which came five days after the gassing, had been controlled by rebel forces. ‘As with other sites,’ the report warned, ‘the locations have been well travelled by other individuals prior to the arrival of the mission … During the time spent at these locations, individuals arrived carrying other suspected munitions indicating that such potential evidence is being moved and possibly manipulated.’ Still, the New York Times seized on the report, as did American and British officials, and claimed that it provided crucial evidence backing u