He began theater work as a call boy, or stagehand, at McVicker's Theatre in Chicago.

[3][4][5] On tour with Laura Keene's stage company in 1865, he had recently gained the title role in the company's production of Tom Taylor's play Our American Cousin, playing the role of Asa Trenchard.

[citation needed] At about 10:14 pm, Harry Hawk was alone on stage in Washington, D.C., on April 14, 1865, delivering what was considered one of the funniest lines of the play.

Hysterical laughter began permeating the theater, and Lincoln was laughing at this line when he was shot.

Hawk was detained by the police and held on $1,000 bond, which Doctor Brown (the undertaker who later embalmed Lincoln) furnished for him.

He was then brought to the Petersen House across the street from the theatre (where Lincoln lay dying), and confirmed to the police that Booth had been the assailant.

Corporal James R. Tanner recorded the following testimony from Hawk: I was on the stage at the time of the firing & heard the report of the pistol.

I heard something tear & somebody fell & as I looked towards him he came in the direction in which I was standing & I believe to the best of my knowledge that it was John Wilkes Booth.

[9]Hawk wrote to his parents on April 16: This is the first time I have had to write to you since the assassination of our dear President on Friday night, as I have been in custody nearly ever since, I was one of the principal witnesses of that sad affair, being the only one on the stage at the time of the fatal shot.

I was playing Asa Trenchard, in the "American Cousin," The "old lady" of the theatre had just gone off the stage, and I was answering her exit speech when I heard the shot fired.

I turned, looked up at the President's box, heard the man exclaim, "Sic semper tyrannis," saw him jump from the box, seize the flag on the staff and drop to the stage; he slipped when he gained the stage, but got upon his feet in a moment, brandished a large knife, saying, "The South shall be free!"

He made his escape out of a door, directly in the rear of the theatre, mounted a horse and rode off.

The above all occurred in the space of a quarter of a minute, and at the time I did not know that the President was shot; although, if I had tried to stop him, he would have stabbed me.

At half-past three I was called by an aid of the President, to go the house where he was lying, to give another statement before Judge Carter, Secretary Stanton, and other high officials assembled there.