Dave Nershi was finalizing a report he'd worked on for months when an ominous email appeared in his inbox. Nershi had worked as a general engineer for the Internal Revenue Service for about nine months. He was one of hundreds of specialists inside the IRS who used their technical expertise -- Nershi's background is in chemical and nuclear engineering -- to audit byzantine tax returns filed by large corporations and wealthy individuals. Until recently, the IRS had a shortage of these experts, and many complex tax returns went unscrutinized. With the help of people like Nershi, the IRS could recoup millions and sometimes more than a billion dollars on a single tax return. But on Feb. 20, three months shy of finishing his probationary period and becoming a full-time employee, the IRS fired him.