A secretive U.S. Drug Enforcement Administration unit is funneling information from intelligence intercepts, wiretaps, informants and a massive database of telephone records to authorities across the nation to help them launch criminal investigations of Americans. Documents reviewed by Reuters show that law enforcement agents have been directed to conceal how such investigations truly begin-not only from defense lawyers but also sometimes from prosecutors and judges. The undated documents show that federal agents are trained to recreate" the investigative trail to effectively cover up where the information originated, a practice that some experts say violates a defendant's constitutional right to a fair trial. If defendants don't know how an investigation began, they cannot know to ask to review potential sources of exculpatory evidence-information that could reveal entrapment, mistakes or biased witnesses. "I have never heard of anything like this at all," said Nancy Gertner, a Harvard Law School professor who served as a federal judge from 1994 to 2011. Gertner and other legal experts said the program sounds more troubling than recent disclosures that the National Security Agency has been collecting domestic phone records. The NSA effort is geared toward stopping terrorists; the DEA program targets common criminals, primarily drug dealers. "It is one thing to create special rules for national security," Gertner said. "Ordinary crime is entirely different. It sounds like they are phonying up investigations."