Answer:
The person who discovered that John Wilkes Booth killed Abraham Lincoln on a ferry and helped the men reach a farm for safety was a Union soldier named Thomas P. "Boston" Corbett. After Lincoln's assassination, Corbett was among the Union soldiers who were assigned to capture Booth and his accomplices. On April 26, 1865, Corbett and other Union soldiers surrounded a tobacco barn on a farm in Port Royal, Virginia, where Booth and his accomplice David Herold were hiding.
Booth refused to surrender and Corbett, who was positioned outside the barn, shot him through a crack in the barn's wall. Booth died a few hours later. Herold surrendered and was later tried and hanged for his role in the assassination.
Corbett later told authorities that he shot Booth because he believed that Booth was about to shoot him or one of his fellow soldiers. Corbett was initially arrested for violating orders not to kill Booth, but he was later released without charges.
It is worth noting that there are some variations in the details of the events surrounding Booth's capture and death, and there is some controversy over Corbett's actions and motives. Nonetheless, it is generally accepted that Corbett played a significant role in Booth's capture and the end of the manhunt for the Lincoln conspirators.