A woman walks Friday at the site of a crashed Malaysia Airlines passenger plane near the village of Rozsypne in eastern Ukraine. (Dmitry Lovetsky/Associated Press)

President Obama on Friday said the U.S. government is confident that someone in separatist-held territory in eastern Ukraine shot down Malaysia Airlines flight 17. He said that Russia supplied the rebels with heavy weaponry, anti-aircraft armaments and sophisticated training they would need to shoot down high-flying planes. And he repeatedly called for a full and thorough investigation into the attack. European leaders, meanwhile, are discussing the imposition of broader sanctions on Russia, but they have also signaled that they are waiting for an international inquiry to turn up more facts.

Yet calls for and a focus on the coming crash investigation cannot become pretext to delay or weaken new sanctions.

There is some logic in placing focus on a forensic examination of the crash, rather than on the injustice of the ongoing, messy civil conflict that has raged in eastern Ukraine for months. The claims of Russian spinners gamely attempting to deflect blame and the volatile behavior of the separatists, who, according to Western news reports, fired warning shots at OSCE investigators who attempted to tour the crash site on Friday, will contrast with straightforward international fact-finding. Separatist and Russian behavior in the region will look only more outrageous.

But U.S. intelligence and several other sources appear to be well on their way to answering the biggest questions about the crash. Many lines of evidence point to pro-Russian rebels firing the shot, with Russia either directly or indirectly implicated in the attack. Obama already offered what amounts to a general but firm attribution of blame.

Even if that weren’t so, airline crash investigations can take a lot of time in ideal circumstances. In the case of MH17, eastern Ukrainian locals, including separatists, seem to have severely compromised the crash site. It’s unclear where the plane’s black boxes are. At least one may be on its way to Moscow. Russia’s contributions to the context in which the MH17 tragedy happened, meanwhile, are reason enough to justify a strong Western reaction: repeatedly and brazenly violating Ukrainian sovereignty, stirring up pro-Russian extremists and sending arms across the border.

Russia deserved tough treatment before MH17. It deserves a swift and hard reaction now — beyond the sanctions the United States announced earlier this week, and well beyond the more limited response European nations have so far pursued.

Stephen Stromberg is a Post editorial writer. He specializes in domestic policy, including energy, the environment, legal affairs and public health.