The gas Russian authorities used at the end of a Moscow hostage crisis, which killed 116 of the captives, was the anesthesia fentanyl or another drug related to it, U.S. officials said Tuesday.
In Moscow, U.S. Ambassador Alexander Vershbow offered the first official American criticism of the Russians' continued refusal to identify the substance used.
"It's clear that perhaps with a little more information, at least a few more of the hostages may have survived," Vershbow said.
Russian authorities pumped the gas into a theater where separatist rebels were holding more than 800 people hostage Saturday. The gas killed 116 hostages; 50 hostage-takers also died, many from gunshot wounds.
Relatives of Oklahoman Sandy Booker, 49, said Russian authorities notified them Tuesday that Booker was among the dead.
Based on reports from doctors who visited some of the American hostages, U.S. officials believe the gas was an opiate — a drug related to morphine and heroin, Vershbow said. Other U.S. officials identified the drug as fentanyl, commonly used in anesthesia and to relieve severe pain.
Fentanyl is a fast-acting narcotic that in large doses can shut down breathing and cause death from lack of oxygen. A hundred times more potent than morphine, fentanyl also has been abused for the highs it produces.
The effects of opiates like fentanyl can be reversed with the drug naloxone, known by the brand name Narcan. U.S. officials say some of the hostages responded to doses of Narcan, which bolstered the belief that the Russians used an opiate to knock out the hostage-takers and their captives.
Fentanyl was among drugs that Pennsylvania State University researchers suggested two years ago the U.S. military explore as weapons to subdue angry mobs. The Pentagon has put such research on hold, however, because of worries that it would violate the international ban on chemical weapons.
Whether Russia's use of the gas in the hostage situation would violate the treaty is unclear, since the pact allows for the use of chemical agents for law enforcement purposes.
At the White House, spokesman Ari Fleischer avoided criticizing the Russian government's response to the hostage crisis.
"The president feels very strongly that responsibility for this rests with the terrorists who took these people hostage and put them in harm's way in the first place," Fleischer said.