The Department of Justice has always had the power to investigate federal crimes, but it didn't always have the means to do so. In the 19th century, government agencies often hired private detective firms such as the Pinkertons to solve crimes [ref]. In 1908, Illegal land sales in the western United States angered President Theodore Roosevelt, who then gave Attorney General Charles J. Bonaparte the authority to create a small bureau of detectives to investigate these crimes. By 1909, they were given an official name: The Bureau of Investigation.
Initially, very few crimes were under the Bureau's jurisdiction. Land fraud, national bank scams, anti-trust crimes and criminals who crossed state lines were under the Bureau's purview. Over the next decade, new laws expanded the scope of the federal government to investigate national crimes, and the number of agents increased as well. During World War I, agents focused on stopping espionage and sabotage, and cracking down on men who avoided the draft. By the 1920s, there were more than 300 agents and 300 support personnel operating a growing number of field offices [ref].
Until the early 1920s, unprofessional agents who were poorly trained and unqualified for their jobs plagued the Bureau of Investigation. Politics was a strong influence, and agents could be easily bribed to overlook crimes. Agents sometimes gathered incriminating information to discredit political opponents [ref, ref]. All that began to change in 1924, when Attorney General Harlan Fiske Stone elevated 29-year-old Assistant Director J. Edgar Hoover to the office of Director. Hoover immediately began reviewing procedures and agent records. He personally reviewed every agent's file, and was amazed at how many agents were on staff solely because of political connections or favors. He fired more than 100 of them within a few months [ref]. Then, Hoover raised the standards for hiring new agents, requiring college educations and law enforcement experience. He created rules and regulations for agent conduct and investigative procedure, ensuring that Bureau activity would be uniform across the nation. As Hoover put it, "We all should be concerned with only one goal -- the eradication of crime."
Hoover was also responsible for many reforms in the field of criminal investigation. He created the FBI Crime Lab in 1932, and opened a training academy in 1935, the same year the Bureau became the Federal Bureau of Investigation. This academy trained FBI agents as well as numerous local and state police officers. Another Hoover innovation was the Ten Most Wanted list. Created in 1950, this list provides photos and information on the ten fugitives (in no particular order) the FBI most wants to catch, and is posted in public places such as post offices. As of 2002, 458 people had been shown on the list, and 429 had been captured. Today, the Ten Most Wanted list is available online.
Through World War II and into the Cold War, the FBI continued to take on new duties under Hoover's guidance. The Bureau investigated German and Japanese spies during the war and rooted out Communists in the post-war years. The FBI's priorities changed once again in the wake of the 9/11 attacks; now, counterterrorism is a top priority. The Bureau tracks known terrorists and cooperates with other agencies, such as the CIA, and intelligence and law enforcement agencies from other countries to gather information. Unlike many other government agencies, the FBI was not folded into the Department of Homeland Security -- it continues to operate within the Department of Justice.