For years, Arpaio has been accused of discriminating against Latino residents by targeting them during immigration raids. DOJ's investigation began during the Bush administration in 2008 and was publicly disclosed in March 2009. Arpaio held up the investigation by refusing to turn over records, leading the Justice Department to sue him in September 2010.
Federal officials aren't expected to announce a lawsuit today. Their report will focus on whether Arpaio's office had a pattern or practice of discriminating against Latinos. Ideally, they would reach an agreement with Arpaio's office and he would institute a number of reforms to relieve their concerns. But given Arpaio's defiance of the feds so far, that prospect seems unlikely.
DOJ's announcement of the press conference had been embargoed, but the Arizona Republic had a story about the press conference on Thursday morning.