Congress has released a report of the hearings:
http://oversight.house.gov/images/st...ATF_Report.pdf
Much more at the link. The gist of the report is that the ATF already had the goods on the straw purchasing rings and the field agents were told to let guns walk to try and get evidence on more conspirators in the ring. The effort to catch more folks failed and the guns started showing up at crime scenes. Field agents and gun dealers repeatedly raised alarms that were ignored. After the scandal was exposed by field agents, the DoJ began lying to Congress to cover up their mistakes.