<blockquote>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</blockquote>
via <a href="http://www.reuters.com/article/2013/08/05/us-dea-sod-idUSBRE97409R20130805">Exclusive: U.S. directs agents to cover up program used to investigate Americans | Reuters</a>.