The Chinese government froze meaningful efforts to trace the origins of the coronavirus pandemic, despite publicly declaring it supported an open scientific inquiry, an Associated Press investigation has found.

The AP drew on thousands of pages of undisclosed emails and documents, leaked recordings, and dozens of interviews that showed the freeze began far earlier than previously known — in the first weeks of the outbreak — and involved political and scientific infighting in China as much as international finger-pointing.

Crucial initial efforts were hindered by bureaucrats in Wuhan trying to avoid blame who misled the central government; the central government, which silenced Chinese scientists and subjected visiting U.N. officials to stage-managed tours; and the World Health Organization itself, which may have compromised early opportunities to gather critical information, according to internal materials obtained by AP.