The best summary of a Federal Tax Prosecutor comes from the book: Convictions: A Prosecutor’s Battles Against Mafia Killers, Drug Kingpins, and Enron Thieves
by John Kroger, which can be found here. The section from the book is paraphrased as follows:
In the United States today few people possess more power. As early as 1940 Supreme Court Justice Robert Jackson remarked that a federal prosecutor has “more control over life, liberty and reputation than any other person in America.” Since Jackson’s day, that power has only increased. In the words of federal judge (and former AUSA) Gerald Lynch, “Congress has cast the federal prosecutor in the role of God.” Hyperbole? Certainly—but a revealing comment nevertheless.
Federal prosecutors have not always had so much influence. Traditionally, crime was the responsibility of state and local governments. Federal criminal law was a sleepy and unimportant backwater. Starting in the 1950s, however, Congress passed a series of landmark crime bills that radically expanded the United States government’s role in combating crime. These bills gave federal prosecutors, for the first time in our nation’s history, the legal tools they needed to combat the nation’s most serious criminal threats: the mafia, corrupt corporate executives, gangs, and drug dealers. As a result, the federal government is now deeply involved in law enforcement in your community.
During the exact same period, Congress, the Justice Department, and the federal courts quietly revolutionized law enforcement in a second, more subtle way. Back in the old days the federal government observed a strict division of labor: agents investigated crimes, and then prosecutors handled cases in court once those investigations were completed. Today that is no longer true. Disturbed by revelations of domestic political spying by J. Edgar Hoover’s FBI and believing, rightly or wrongly, that lawyers would respect civil liberties more carefully than would gumshoe agents, America’s lawmakers gradually shifted investigative power from law enforcement agencies like the FBI to federal prosecutors. As a result of this transfer of power, federal agents today cannot obtain a wiretap, a search warrant, an arrest warrant, an immunity order, or most subpoenas—the basic investigative tools required in every major case—without cooperation and prior approval from an AUSA. This gives AUSAs a virtual veto over most federal investigations. In some parts of the country federal prosecutors use this leverage lightly, and agents still run the show. But in most big cities and in all the most important federal cases AUSAs tell agents politely but firmly, “Investigate the case my way, or you won’t investigate at all.” As a result, AUSAs today are not just courtroom attorneys; they have become our nation’s chief criminal investigators.