Where was John Surratt on April 14, 1865 ?

[RJNorton]

Mike Kauffman writes in American Brutus (p. 224) that Booth was already at the boardinghouse when Mary and Weichmann returned.

He writes, "A few blocks away (from Ford's Theatre) Mary Surratt returned from the country and found Booth waiting in her parlor. They talked in private, and in a few minutes, Booth left. He rode into Baptist Alley, and dismounted by the back door of the theater."

There is no footnote for Booth already being at the boardinghouse when Mary and Weichmann returned. Where did Mr. Kauffman get this information? Anyone know?