European Union foreign ministers meet in Brussels today, facing the challenge of proving Russia's role in the downing of the Malaysia Airlines flight MH17 and then agreeing on how to punish the Kremlin.
The talks are likely to culminate in a new ratcheting of sanctions against Russia's economy, although by how far remains unclear.
France, Germany and Britain say the time is ripe for getting tougher. After talking at the weekend to President Francois Hollande and German Chancellor Angela Merkel, British Prime Minister David Cameron said the three "agreed that the EU must reconsider its approach to Russia and that foreign ministers should be ready to impose further sanctions.
"If Russia does not immediately take the necessary measures, consequences will be decided by the European Union when its foreign affairs council meets [today]," Hollande's office said, rather more cautiously.
Fraser Cameron, of the Brussels-based EU-Russia Centre think-tank, said the atrocity had strengthened the case to bite deeper into Russia's financial and business interests.
At present, sanctions - imposed after the seizure of Crimea - are at a relatively low level, comprising visa bans and asset freezes on more than 60 "targeted individuals" in the Russian elite and pro-Russian Ukraine separatists in Slaviansk, Luhansk and Donetsk.
Those targeted included Vyacheslav Volodin, a top aide to Putin, and Vladimir Shamanov, the commander of Russian airborne troops that took part in the occupation of Crimea.
"Throughout Europe there is a mix of outrage at the behaviour of the separatists at the crash site and sympathy for the enormous loss of life, especially the many Dutch families who had been blown out of the skies," Cameron said.
"Unless Putin changes tack in the next 24 hours, EU ministers will almost certainly agree new sanctions ... This will not be at the top end of the scale but sufficient to damage the Russian economy." At the core of any decision is ascertaining proof of Russian crime.
The accusations of a Russian role come from Ukraine and the US, mostly through its surveillance satellites, something that Russia will argue is a sign of manipulation and a desire to return to the Cold War.
Despite its anger, Europe is keenly aware of its own weaknesses with regard to Russia.
France is facing criticism over a controversial 1.2 billion ($1.92 billion) contract to sell Russia two advanced Mistral-class helicopter carriers, a deal negotiated by Hollande's predecessor, Nicolas Sarkozy. Just three weeks ago, more than 400 Russian sailors arrived at Saint-Nazaire in western France to undergo a four-month training session on the high-tech ship. The first vessel is due to be delivered in October.
Britain's economy, especially the City of London financial centre, also has big interests in keeping Russia onside. Russia is one of the biggest export markets for Germany's manufacturing industry. And former Soviet EU members depend on Russian gas to keep their homes, offices and factories lit and warm.
A day before the plane disaster, US President Barack Obama fired a new volley of sanctions targeting Russia's finance, defence and energy sectors in retaliation for Moscow's support of the separatists.
European leaders met the same day but stalled, choosing instead to postpone any decision until the end of the month.
They had been preparing to review loans being negotiated with Moscow by two powerful investment arms, the European Bank for Reconstruction and Development and the European Investment Bank, which offer low-interest credit for development projects.