A new study by a professor at the Massachusetts Institute of Technology and an analyst at a military contractor claims that the munitions used in the August 21 chemical weapons attacks near Damascus were fired from multiple sites and had a maximum range of 3.5 kilometers (2.2 miles).

The Violations Documentation Center has documents the deaths of at least 900 civilians in the attacks on several insurgent-held areas in East Ghouta and West Ghouta.

Professor Theodore A. Postol and Richard M. Lloyd of Tesla Laboratories, working with videos and photographs, argued that the rockets were propelled by motors taken from “Grads”, 122-millimeter conventional artillery.

The Grad, or BM-21, originated in the Soviet Union but has been reproduced and updated by many countries, including Russia, China, Egypt, and Iran. Both the Syrian army and insurgents possess them.

Eliot Higgins, who has evaluated the chemical weapons attacks on his Brown Moses blog, said the conclusion fit his analysis of an assault by the Syrian military: “A range of beyond 2.5 kilometers (1.6 miles) would put potential launch sites in an area between Jobar and Qaboun, to the north and northwest of the impact locations, that has been a hive of government activity for months.”

Postol had said last month that the maximum range for the rockets was 2 kilometers, challenging the idea that they were fired from regime-held sites.

In September, both The New York Times and Human Rights Watch, drawing from the findings of United Nations investigators, estimated a range of 9 kilometers (5.6 miles) from the reported compass headings for two rockets.

The published range for a Grad rocket is about 20 kilometers, or 12.4 miles.

However, Postol said the range of the August 21 rockets would have been undermined by their large mass and drag. He said that, as a sarin-filled rocket was pushed to greater air speeds, the stresses created by its non-aerodynamic shape could cause it to tumble or break apart.

Lloyd said that his separate analysis of the reported impact sites suggested that two to four launchers were involved in the August 21 strikes.

Dr. Postol agreed, “The line of impacts suggests a launcher that changed loft angle. This is consistent with a strategy aimed at spreading the nerve agent over a wide area.”

Lloyd and Postol have previous calculated that the rockets held about 13.2 gallons of sarin, a far larger amount than initially suggested after August 21. The UN came to a similar conclusion in September.