A declassified French intelligence assessment of the most recent chemical weapons attack in Syria puts to rest suspicions that a nerve agent was deployed by either rogue elements in Bashar Assad’s regime or even the rebels fighting to overthrow him.

Syrian opposition activists accused the regime two weeks week ago of gassing hundreds of civilians in a suburb of the capital Damascus. French president François Hollande said last week there was no doubt the gas had been used by the regime and vowed to “punish” those responsible.

With Britain’s Parliament voting against intervention in the Syrian conflict last week, France is among few Western allies that are still prepared to support the United States in any punitive strike they decide to undertake against the Middle Eastern country where a civil war has raged for more than two years.

Although Islamist rebels in Syria might also possess chemical weapons and had an incentive to deploy them — to trigger American involvement in the war as President Barack Obama warned last year that the use of poison gas would cross a “red line” — Foreign Policy‘s David Kenner argues that the French report (PDF), released on Monday, leaves little doubt that the regime did, in fact, deploy sarin gas.

“The sarin is stored in binary form,” the report says, “the two chemical precursors necessary to make the gas are kept separate and only mixed immediately before use.” This technological sophisticated may turn out to be a key point when United Nations investigators release their finding about the Damascus attack.

If they find that the toxic agent used in the attack was an advanced form of sarin — containing chemical stabilizers and dispersal agents — the weapon will most likely have come from Syrian regime stockpiles.

The French also leave little ambiguity about Assad’s culpability. Only the president and top members of his regime have the authority to order the center where Syria’s chemical weapons are kept to employ them. This unit, moreover, is “composed solely of Alawite military personnel,” according to French intelligence — members of Assad’s Shia tribe who have been altogether loyal to his government for fear of the Sunni majority in the country taking power.

Skepticism also stemmed from Assad deploying the gas less than three days after United Nations inspectors arrived in his country to investigate previous allegations of chemical weapons use. Why would he deploy a nerve agent while investigators were in the country? Especially when the American president had suggested such use would trigger an international response?

The French believe Assad’s position in the capital and surrounding neighborhoods was threatened by a persistent rebellion in the suburbs. The attack, they believe, was designed to “secure strategic sites,” including the Mezzeh military airport. The fact that the government launched a conventional weapons offensive into the same areas after the suspected sarin gas attack took place supports that assessment.