A Seattle researcher says he has uncovered data on early COVID-19 cases that appears to have been mysteriously deleted from a major database, The New York Times reports. Jesse Bloom, a virologist at the Fred Hutchinson Cancer Research Center, detailed the discovery in a new study that argues the deleted data—genetic sequences from hundreds of virus samples collected by Wuhan University scientists—means researchers who are currently trying to determine the origin of the pandemic don’t have the full picture. Bloom said he found 13 sequences of the virus on Google Cloud after they had apparently been deleted from the Sequence Read Archive, a public repository for DNA sequencing data managed by the National Library of Medicine. All in all, he said, he found that 241 sequences of the virus had been deleted from the database.

Bloom now believes those were intentionally removed, writing in his paper that it “seems likely that the sequences were deleted to obscure their existence.” Other scientists remain skeptical, however, especially as Bloom’s study has not been peer-reviewed. “I don’t really understand how this points to a cover-up,” Stephen Goldstein, a virologist at the University of Utah, told the Times. Goldstein pointed out that the same Wuhan scientists who had originally uploaded genetic sequences had published all their findings elsewhere, meaning all the most critical information is still available, even if the full sequences are not.