Just before leaving Syria late last month, U.N. weapons inspectors discovered an odd-looking projectile sticking out of the dirt near the spot where hundreds of Syrians died Aug. 21. Experts who studied the device would call it a “trash can on a rocket,” citing its long fuselage and fat warhead capable of carrying 15 gallons of poison.

The reference to the rocket’s discovery would take up only a few lines in Monday’s highly technical U.N. report confirming the use of lethal sarin gas against Syrian civilians. But the new details about one of the weapons allegedly used in the attack came closer than ever to pinning the blame on the Syrian government, diplomats and weapons experts said.

The 41-page U.N. report concluded that much of the sarin used in the attack was hurled east of Damascus in unusually shaped, 330mm artillery rockets, similar to the one found protruding from the soil in the Zamalka suburb. The finding is significant, weapons experts say, because the rockets appear to be of a unique Syrian design, different from any of the shells and warheads associated with other producers of chemical arms.

“The U.N. report provides solid confirmation as to the two types of rockets used in the attack, and its evidence provides even greater proof that the government was responsible,” said Peter Bouckaert, emergencies program director at Human Rights Watch, which last week issued a study that also pointed to the rockets as vital clues linking the Syrian regime to the attack.

Although the U.N. report does not explicitly assign blame, Bouckaert said, its findings “point even more convincingly towards Syrian government responsibility,” citing not only the rockets’ remnants but also their flight path and the military-grade quality of the sarin that they contained.

“It points the finger directly at them,” he said.

The U.N. team’s report was the first official document to confirm the use of the unusual rockets, which have been cited in several reports by human rights activists and weapons experts who analyzed images of rocket motors and other parts found in neighborhoods hit by toxic gases in the pre-dawn hours of Aug. 21. Chemical warheads typically contain only a small amount of explosives — enough to disperse, but not incinerate, their toxic contents — and several of the rockets were relatively intact when U.N. investigators toured the affected neighborhoods last month.

In the Moadamiya suburb, inspectors found the remains of several Russian-made 140mm rockets, many of them bearing identification plates and engravings in the Cyrillic script, according to the U.N. report. It said the larger, 330mm rockets were found in Zamalka and Ein Tarma, two southeastern neighborhoods that recorded the highest numbers of casualties.

Researchers who have studied the weapons used during the Syrian conflict confirmed that the 330mm rockets have been used rarely, and always by government forces.