Over the weekend, leaders from Europe, the United States, Australia, and Malaysia have had blunt phone conversations with Putin. They have asked him to use his influence on the pro-Russian rebels in Ukraine to allow investigators unhindered access to the site of the wreckage. Putin, finally, agreed to fully cooperate and called for a robust investigation.

But when? Is this yet another delaying tactic to preempt sanctions? And if Putin insists that the rebels did not shoot down MH17, then what has he to hide when it comes to ordering the rebels to hand over the flight’s black box? It is all too clear that the longer the rebels and Russian intelligence experts have access to the site, the more the evidence will be contaminated. This is a damning indictment of Putin’s worldview.

This is not the time to give Putin more time. European leaders have been making that mistake repeatedly since Russia annexed Crimea in March. Not only have most European leaders de facto accepted the annexation of Crimea, they have encouraged Russia to meddle and destabilize eastern Ukraine even further—precisely because the European response has been weak and divided and the two rounds of sanctions were simply insufficient to change Putin’s mind.

Instead, the Europeans dispatched the OSCE to eastern Ukraine and established a special contact group to negotiate with the rebels. But the OSCE, despite all the goodwill, is toothless because it lacks the political means to change Europe’s policy toward Russia. It showed the helplessness of their efforts when armed rebels took unarmed OSCE diplomats hostage in April.

After all the mistakes and hand-wringing by European leaders over the situation in eastern Ukraine, and now the downing of a commercial aircraft, this surely is the time to act decisively. Tough sanctions should be imposed immediately. Yes, it will give Putin even more of an opportunity to rail against the West and again resort to calling the government in Kiev a bunch of fascists. And yes, his domestic ratings will go up even further. But none of this is new.

Furthermore, with a huge show of political will, all the countries that had citizens on board MH17 should agree to send investigators, together in large numbers and in protected vehicles, to the crash site. This is Ukrainian territory. This will demand nerves of steel. But now is the time to hold and act together—and not waver, which Putin expects.