Experts say Russian authorities failed to heed the alarms set off by terror attacks in Russia's heartland over the past couple of years, including a deadly 2009 blast that hit a luxury train near St. Petersburg and a twin suicide bombing in Moscow's crowded metro last March that killed almost 40 people.
"When it happens, we see authorities react. They give instructions and order intensive antiterrorist operations, but it all comes to naught until we are shaken by the next explosive terrorist act," he said.
New wave of militants
Chechen warlord Doku Umarov, one leader of the new wave of Islamist militants who have supplanted the Chechen separatists of the past, claimed responsibility for the Moscow metro bombings and is widely cited as a suspect in Monday's Domodedovo blast.