There’s no more mystery. Not for the West, anyway. Though the Egyptian-led investigation is far from over, leaks from the British, the U.S., and the Egyptian investigative team itself have put enough information in the public domain to be able to draw some pretty safe conclusions.

The black box from Russian Metrojet Flight 9268 shows there was an explosion onboard caused by a bomb (as opposed to a fuel line explosion organic to the plane). A review of U.S. and British SIGINT intercepts show the Islamic State discussing the attack prior to and after the downing of the plane. The Americans and British, in an extraordinary step, shared their intelligence intercepts with the Russians, who immediately halted all Russian flights to and from Egypt. This was a 180° turn from Russia’s stance the day before the Western intelligence was shared; Russia had insisted any suggestion the crash was attributable to terrorism was premature. The IS has now issued a third claim of responsibility for the bombing, asserting that they specifically targeted the Russian plane due to Russia’s involvement in the war in Syria.

How they did it is still up for speculation (the most likely scenario is that an airport worker at Egypt’s Sharm el Sheikh airport was compromised and put the bomb in the cargo hold), but there’s little doubt the Islamic State successfully committed the largest international terror attack since September 11, 2001.

The Russians aren’t happy about admitting it so quickly, though. The Kremlin’s propaganda machine has been focused on exhorting the modernity of the Russian military as it safely and surgically destroyed Islamic terrorists in Syria. Now it has to switch gears from glowing reports of military capability to spinning this new vulnerability into public support for a more protracted conflict, despite the threat to Russian citizens. Multiple Russian blogs are claiming the U.S., the Brits, or the Saudis (or some combination thereof), are responsible for the downing of the Metrojet flight. The Russians will likely encourage this kind of disinformation until the Kremlin can develop a cohesive anti-IS message that suits its goals.

Eventually, though, Russian President Vladimir Putin will have to respond to ISIS, just as the United States had no choice but to respond to al-Qaeda in Afghanistan after 9/11. Anti-Western rhetoric suits Moscow’s needs for the moment, but Putin certainly realizes that if the Islamic State can pull together an attack like this in a month (Russia began bombing in Syria in late-September), more attacks will follow. At some point it will be obvious to even media-isolated Russians it is the Islamic State, not the CIA, who is attacking Russians.

The rest of the world will, of course, focus on their own security in their own ways, but the Russians were specifically targeted, putting immense pressure on Russia’s strongman to act. Putin has invested enormous resources over decades to obliterate Islamic terrorists targeting Russia.

A great deal of Putin’s early political success was due to his response to Chechen Islamic terrorist attacks in the late ’90s and the 2000s as the Second Chechen War dragged on. Islamists bombed Russian apartment buildings and trains, attacked a theater, and took over 1000 people hostage at an elementary school in Beslan. At least 330 people died at Beslan, including 186 children.

Putin cast himself as the ultimate hard-liner against Islamic terrorism. He built his reputation as being ruthless and uncompromising. The brutal pacification of Chechnya while Putin was Russia’s prime minister and then president was supposed to be the ultimate deterrent against future attacks on Russia and Russian interests.