Lafayette C . Baker Lafayette Curry Baker ( October 13 , 1826 – July 3 , 1868 ) was a United States investigator and spy , serving for the Union Army , during the American Civil War and under presidents Abraham Lincoln and Andrew Johnson . Baker ' s exploits are mainly known through his book " A History of the Secret Service " which he published in 1867 after his fall from grace . During the Civil War , he spied for General Winfield Scott on Confederate forces in Virginia . Despite numerous scrapes , he returned to Washington , D . C . , with information that Scott evidently thought valuable enough to raise him to the rank of captain and he swiftly took over charge of the Union Intelligence Service from the Scottish detective Allan Pinkerton . Baker largely owed his appointment to Secretary of War Edwin M . Stanton , but suspected the secretary of corruption and was eventually demoted for tapping his telegraph lines and packed off to New York . He was quickly recalled , however , after the assassination of President Lincoln in 1865 . Within two days of his arrival in Washington , Baker ' s agents in Maryland had made four arrests and had the names of two more conspirators , including the actual presidential assassin John Wilkes Booth . Before the month was out , Booth along with David Herold were found holed up in a barn and Booth was himself shot and killed by Sgt . Boston Corbett . Baker was promoted to the rank of brigadier general and received a generous share of the $ 100 , 000 reward offered to the apprehender of the president ' s killer . The following year , however , Baker was sacked from his position as government spymaster . President Johnson accused him of spying on him , a charge Baker admitted in his book which he published in response . He also announced that he had had Booth ' s diary in his possession which was being suppressed by the Department of War and Secretary Stanton . When the diary was eventually produced , Baker claimed that eighteen vital pages were missing . It was suggested that these would implicate Stanton in the assassination . Baker died in 1868 , supposedly from meningitis . As it was scarcely eighteen months after his explosive allegations , some suggested he was killed by the War Department to silence him . Using an atomic absorption spectrophotometer to analyze several hairs from Baker ' s head , Ray A . Neff , a professor at Indiana State University , determined the man was killed by arsenic poisoning rather than meningitis . Baker had been unwittingly consuming the poison for months , mixed into imported beer provided by his wife ' s brother Wally Pollack . " The Lincoln Conspiracy " by Balsiger and Sellier cites a diary Baker ' s wife kept which chronicled several dates Pollack brought Baker beer ; they correspond to the gradually elevated levels of toxin in the Baker hair samples Neff studied . Wally worked for the War Department , though whether he acted on orders or alone has yet to be determined . Nevertheless , Neff ' s studies , along with the information chronicled in Baker ' s diary , serve to bolster a cogent and provocative alternate history of the Lincoln assassination , one distinct from the chronology most commonly promulgated by mainstream U . S . historians . Baker was born in Stafford , New York and is buried in Forest Hills Memorial Park Huntingdon Valley , Pennsylvania . His unmarked grave can be found behind the Hanover - Kensington Memorial plot .