Mr. Plant was a native of Washington, and for many years was a justice of the peace and notary public. In early life he was active in military matters connected with the American Rifles and President's Mounted Guard.

Plant testified in defense of Edwin Spangler, a stagehand at Ford's Theater. Plant was a dealer in furniture and a paperhanger, and had been engaged in cabinetwork at the time of the conspirators' trial. He lived at 350 D Street NW. Plant gave testimony about the condition of the locks on Boxes 7 and 8 in Ford's Theatre, which comprised the Presidential Box. He also testified about the hole in the door of Box 7. There was doubt concerning who made the hole--John Wilkes Booth or Edwin Spangler. If Booth had indeed made the hole, the question arose as to whether Spangler had any knowledge of it.