On July 15, 2011, Attorney General Eric Holder issued a memo saying he concludes "that the law requires the application of the [Fair Sentencing] Act's new mandatory minimum sentencing provisions to all sentencings that occur after August 3, 2010, regardless of when the offense conduct took place." He directs prosecutors "to act consistently with these legal principles."
Professor Berman has blogged the issue and provides a link to the memo at:
http://sentencing.typepad.com/sentencing_law_and_policy/2011/07/only-a-year-late-ag-holder-sees-light-and-reverses-course-on-fsa-pipeline-sentencing-issue.html
