It is unclear why they gathered. A police statement said it was to discuss "escalating problems of the criminal world." Some insiders spoke of a conflict between Moscow crime bosses and of a looming mob war reminiscent of the bloody battles of a decade ago.

Whatever the reason, the police said that when leaders of Russia's criminal elite convened on a yacht in the Moscow River recently, the authorities moved swiftly. In black masks, with weapons drawn, commandos pounced from a hovering helicopter onto the roof of the yacht, setting off a media frenzy when they briefly detained 37 men they said belong to the Vory v Zakone, or Thieves in Law.

A mobster caste forged in the Soviet gulags, the Vory v Zakone maintains a hallowed place in Russia's criminal lore, akin to that of the Cosa Nostra in Italy.