But the report’s annexes, detailing what the authors found, were what caught the attention of nonproliferation experts.

In two chilling pieces of information, the inspectors said that the remnants of a warhead they had found showed its capacity of sarin to be about 56 liters — far higher than initially thought. They also said that falling temperatures at the time of the attack ensured that the poison gas, heavier than air, would hug the ground, penetrating lower levels of buildings “where many people were seeking shelter.”

The investigators were unable to examine all of the munitions used, but they were able to find and measure several rockets or their components. Using standard field techniques for ordnance identification and crater analysis, they established that at least two types of rockets had been used, including an M14 artillery rocket bearing Cyrillic markings and a 330-millimeter rocket of unidentified provenance.

These findings, though not presented as evidence of responsibility, were likely to strengthen the argument of those who claim that the Syrian government bears the blame, because the weapons in question had not been previously documented or reported to be in possession of the insurgency.

Moreover, those weapons are fired by large, conspicuous launchers. For rebels to have carried out the attack, they would have had to organize an operation with weapons they are not known to have and of considerable scale, sophistication and secrecy — moving the launchers undetected into position in areas under strong government influence or control, keeping them in place unmolested for a sustained attack that would have generated extensive light and noise, and then successfully withdrawing them — all without being detected in any way.

One annex to the report also identified azimuths, or angular measurements, from where rockets had struck, back to their points of origin. When plotted and marked independently on maps by analysts from Human Rights Watch and by The New York Times, the United Nations data from two widely scattered impact sites pointed directly to a Syrian military complex.