 Booth then jumped from the President 's box to the stage , where he raised his knife and shouted " Sic semper <unk> " ( Latin for " Thus always to tyrants , " attributed to Brutus at Caesar 's assassination and the Virginia state motto ) , while others said he added , " I have done it , the South is avenged ! " Various accounts state that Booth injured his leg when his spur snagged a decorative U.S. Treasury Guard flag while leaping to the stage . Historian Michael W. Kauffman questioned this legend in his book , American Brutus : John Wilkes Booth and the Lincoln Conspiracies , writing in 2004 that eyewitness accounts of Booth 's hurried stage exit made it unlikely that his leg was broken then . Kauffman contends that Booth was injured later that night during his flight to escape when his horse tripped and fell on him , calling Booth 's claim to the contrary an exaggeration to portray his own actions as heroic . 
