Thousands of Ukrainian investigators are scouring crime scenes across the country, as are teams from half a dozen other countries and prosecutors from the International Criminal Court. Workers from local and international nonprofit groups are making their own efforts to document alleged abuses. The Ukrainian government has bused journalists from all over the world into Bucha and other towns around Kyiv. In at least one case, they were permitted to walk through a mass grave site.

Allowing so many to see what happened up close has helped fuel international support—and weapons deliveries—for the Ukrainian cause. But it also risks tainting evidence and, ultimately, undermining efforts to convict Russian troops for alleged war crimes.

Forensic evidence can be tossed out in court if it isn’t handled carefully, experts say, and if victims are interviewed again and again, it risks re-traumatizing them and may make them less useful witnesses at trial since their accounts may vary.

“There are too many cooks in the Ukrainian kitchen,” said one foreign adviser working with prosecutors in Ukraine. “You can’t have too many people trampling over a crime scene.”