After the assassination of Abraham Lincoln, Wood was summoned back to Washington by an urgent telegram from Edwin Stanton to assist in the investigation. Following this, he was sworn in on July 5, 1865, by Secretary of the Treasury Hugh McCulloch to head the newly formed Secret Service for four years until he resigned in 1869. He was considered the best in battling financial crime, and within a year of its founding, the Secret Service had arrested over 200 counterfeiters. He died on March 20, 1903, and was buried in the Congressional Cemetery in Washington, D.C.