As Dr. Anthony Fauci has faced public scrutiny from congressional Republicans, the D.O.J. has pursued a quieter and more expansive effort against a wider circle of researchers.

The investigation, centered in the National Institute of Allergy and Infectious Diseases, has examined research practices and potential conflicts of interest among scientists studying emerging viruses.

Federal prosecutors have reviewed documents related to grant funding and collaborations, though no charges have been filed against Dr. Anthony Fauci or other researchers.

The scope reflects ongoing political and scientific debates over pandemic origins and laboratory safety protocols.