Short answers, pulled from the story.
132 hostages died in the Moscow theater hostage crisis of October 2002. The vast majority died from the effects of the chemical gas used by Russian special forces, not from gunshot wounds. Some estimates put the total civilian death toll higher, with one list containing 204 names and others reaching 300 when including those who died in the following year from gas-related complications.
A 2012 study, and earlier analysis by researchers at the British defense laboratories at Porton Down, Wiltshire, identified the gas as a mixture of carfentanil and remifentanil. Carfentanil is a veterinary large animal sedative, and remifentanil is an anesthetic agent. Russian Health Minister Yuri Shevchenko described it only as based on fentanyl; the government never officially disclosed the full composition.
The attack was led by Movsar Barayev, the nephew of slain Chechen rebel militia commander Arbi Barayev. Military commander Shamil Basayev later posted a statement claiming ultimate responsibility for the operation. Independent investigators also alleged that a figure known as "Abu Bakar," believed to be Khanpasha Terkibayev, exercised real control over the operation and was an FSB agent provocateur.
The hostage-takers demanded the immediate and unconditional withdrawal of Russian forces from Chechnya and an end to the Second Chechen War. They also demanded a halt to artillery and air strikes, an end to zachistka "mopping-up" operations, and a public statement from President Vladimir Putin declaring he was working to end the war. Their stated deadline was one week.
On the 20th of December 2011, the European Court of Human Rights ordered Russia to pay 64 applicants a total of 1.3 million euros in compensation. The court found Russia had violated Article 2 of the European Convention on Human Rights through inadequate planning and conduct of the rescue operation, and through failure to conduct an effective investigation. The court did not find a violation regarding the decision to use force and gas to end the siege.
The crisis was followed by sweeping anti-terrorism legislation that banned publication or broadcast of any statement hindering an anti-siege operation or justifying the aims of hostage-takers. In January 2003, the management of NTV, the last nationwide television channel effectively independent of the government, was replaced, profoundly changing its editorial policy. Legislator Sergei Yushenkov described the new law as effectively legalizing censorship in emergency situations.