A U.S. Senate investigation has uncovered dozens of credible reports of medical neglect and poor conditions in immigration detention centers nationwide — with detainees denied insulin, left without medical attention for days and forced to compete for clean water — raising scrutiny about how the government oversees its vast detention system. The report released by Sen. Jon Ossoff, a Democrat from Georgia, is the second in a series of inquiries examining alleged human rights abuses in the immigration detention system.