 During his tenure as United States Attorney, Brown led an investigation of Walmart for alleged criminal and civil violations related to the corporation's distribution of opioids through its pharmacies.Brown and his prosecutors sought to indict Walmart and individuals within the company for violations of the Controlled Substances Act, alleging that from 2011 until 2017 the company had ignored pharmacists warnings that prescriptions were being filled for “pill mill” physicians for reasons other than legitimate medical treatment.Before it could be indicted, Walmart appealed the matter to Department of Justice officials in Washington, and the Texas prosecutors were told to stand down.