Chinese scientists manipulated lethal viruses under unsafe conditions at the Wuhan Institute of Virology prior to the coronavirus outbreak, fueling suspicions the pandemic was caused by a lab leak, according to a new congressional report.

The Wuhan lab was engaged in “dangerous genetic modification research on coronaviruses at unsafe biosafety levels,” according to the report, authored by the minority staff on the House Foreign Affairs Committee. The report includes revelations about unsafe working conditions at the lab, as well as new information indicating the Chinese government sought to mislead the world about the experiments taking place there. Congressional investigators say researchers at the lab “had the ability to genetically modify coronaviruses as early as 2016 without leaving any trace of that modification.”