Seymour Hersh, one of the best-sourced journalists in America, reports that the Obama administration "cherry-picked" intelligence to justify an attack on the Assad regime, ignoring reports that the sarin gas attack on civilians last August could have been carried out by a fundamentalist rebel group instead.

Writing in the London Review of Books, Hersh explains that various sources in the intelligence community have told him that the Obama administration knowingly ignored valuable intelligence, and even altered past intelligence reports, while moving unilaterally forward with a plan to topple the Assad regime.

Hersh:

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.

Instead of using all available intelligence to come to a conclusion about the perpetrators of the sarin attack, Hersh writes that the administration immediately assumed that Assad was behind the attack, and then went looking for any available intelligence that fit that assumption.

Hersh points to the very real possibility that the rebel group al-Nusra, a fundamentalist group that aims to topple Assad and enforce Sharia law in Syria, was behind the attack. Highly classified documents proved the group was capable of creating sarin gas. At the very least, Hersh writes, they should have been a strong suspect.

Hersh's reporting throws into question Obama's quick reversal on a possible attack on Assad: