U.S. independent police force. The agency was founded in 1850 by Allan Pinkerton (1819-84), former deputy sheriff of Cook county, Ill. It originally specialized in railway theft cases, protecting trains and apprehending train robbers. It solved the $700,000 Adams Express Co. theft in 1856, and in 1861 it thwarted an assassination plot against president-elect Abraham Lincoln. It later participated in anti-labour union activities (see Homestead Strike). It was instrumental in breaking up the Molly Maguires