German doctors say they've identified the mysterious gas Russian authorities used to bring an end to a hostage drama in a theatre in Moscow.

The doctors believe the gas is Fentanyl, a chemical in the same family as morphine and heroin. It can abruptly paralyze the respiratory system.

The bodies of two German nationals were flown back to Germany after the hostage taking ended.

Besides examining blood samples, the German doctors also said that Russian medics attending victims at the theatre were ordered to inject the hostages with the drug naloxone. It's used to treat people who have overdosed on opium derivatives.

Moscow's chief public health officer said Sunday 116 people died from the gas used by the Russian military.

Chechen rebels held hundreds of people hostage while demanding an end to the war in Chechnya.

Despite international speculation, Russia's military still won't confirm the identity of the gas. They maintain it must remain a military secret to prevent future terrorists from arming themselves against the gas.