He was known as "America's Sherlock Holmes" and earned fame for having conducted private investigations into a number of notable incidents, such as clearing Leo Frank of the 1913 murder of Mary Phagan,[1] and for investigating the deadly 1910 Los Angeles Times bombing conducted by members of the International Association of Bridge, Structural, Ornamental and Reinforcing Iron Workers.

Revenge or anger was the suspected motive as Times publisher Harrison Gray Otis was a staunch opponent of labor unions, and the incident was similar to a nationwide series of dozens of earlier but not-fatal bomb attacks that Burns had been investigating for the National Erector Association.

[2] Burns's investigation found the Ironworkers Union leadership knew and approved of over 100 bombings between 1905 and 1910, perhaps the largest domestic terrorism campaign in American history.

[2] Burns was considered well qualified to direct the Bureau of Investigation, and was friends with President Warren Harding's Attorney General Harry M. Daugherty.

[6] At the request of Attorney General Daugherty, Burns sent agents to investigate Montana Sen. Thomas J. Walsh for evidence of criminal wrongdoing.

The investigation was actually a pretext for retaliation; the congressman had been instrumental in opposing oil leases granted by Secretary of the Interior Albert Fall, a friend of Daugherty and fellow cabinet member.

Burns was forced to resign in 1924 at the request of Attorney General Harlan Fiske Stone[7] and on May 10, 1924, J. Edgar Hoover took over the position on a provisional basis.

In November 1927, Harry F. Sinclair went on trial in federal court for conspiracy to defraud the US in the leasing of the Teapot Dome naval oil reserve.