AP Photo/Library of Congress

Dr. Charles A. Leale was the first doctor to treat President Abraham Lincoln after he was shot at a Washington theater on the night of April 14, 1865. Helena Iles Papaioannou, a researcher with the Papers of Abraham Lincoln Project has discovered an original copy of Dr. Leale's clinical 21-page report from the night Lincoln was shot.

Researchers at the Abraham Lincoln Presidential Library are marveling over the historical equivalent of buried treasure: an up-to-now undiscovered account of the night Lincoln was assassinated, written by the first doctor to treat him.

Dr. Charles Leale was a 23-year-old army surgeon who was in attendance at Ford's Theatre when John Wilkes Booth entered the presidential box and shot Lincoln days after the conclusion of the Civil War. 

Abraham Lincoln researcher Helena Iles Papaioannou discovered Leale's account while searching the records of the surgeon general in the National Archives in Washington, DC. The 21-page report is Leale's own retelling of the tragedy, written just hours after the president died the following morning.

Read the original report on NBCChicago.com

"What is remarkable about this newly discovered report is it's immediacy and poignancy," said Daniel Stowell, director of the Papers of Abraham Lincoln project. "You can sense the helplessness Leale and the other doctors felt that night, but it does not have the sentimentality or added layers of later accounts."

The young doctor was sitting just 25 feet away from the Lincoln box, giving him a front-row seat to the tragedy. He then became the first doctor to treat Lincoln, supervising his care until the president's own doctor arrived.

"The theatre was well filled, and the play 'Our American Cousin' progressed very pleasantly until about half past ten," Leale wrote, "when the report of a pistol was distinctly heard."

"About a minute after, a man of low stature with black hair and eyes was seen leaping to the stage beneath, holding in his hand a drawn dagger."

Leale described how Booth had become entangled in the flag draping the front of Lincoln's box in his leap to the stage. Booth broke his leg in the fall.

"I then heard cries that the 'President has been murdered,' Leale wrote, adding that calls of "kill the murderer" and "shoot him" began echoing through the theatre.

AP Photo/Alexander Gardner

Dr. Charles Leale rushed to the upstairs balcony where Abraham Lincoln had been seated after hearing the president had been shot. He was the first to administer aid
immediately following the shooting.

"I immediately ran to the President's box and as soon as the door was opened was admitted and introduced to Mrs. Lincoln, when she exclaimed several times, 'O doctor, do what you can for him, do what you can!'"

Leale said that Lincoln's breathing was "intermittent" and that he could find no pulse. Using a finger, he removed a clot of blood from the bullet wound and said Lincoln's breathing became "more regular."

The doctor described in great detail how he and others carried Lincoln from the box, down the stairs of the theatre and across the street to the Peterson house across the street.

"We placed the President in bed in a diagonal position, as the bed was too short.  As soon as we placed him in bed we removed his clothes and covered him with blankets. While covering him I found his lower extremities very cold from his feet to a distance of several inches of above his knees. I then sent for bottles of hot water, and hot blankets, which were applied to his lower extremities and abdomen."

Leale said Mary Todd Lincoln entered the room "three or four times" during the evening and that the president's son, Robert Todd Lincoln, remained at his bedside throughout the night. Unmentioned in the report, but well known to history, is the fact that the First Lady was eventually expelled and kept from the room, her grief was so intense.

After hours of futile efforts to save the fallen president, Leale described Lincoln's final moments.

"At 7:20 a.m. he breathed his last, and 'the spirit fled to God who gave it.'"

Leale had received his medical license only six weeks earlier. At the time of the assassination, he was in charge of a wounded officers' ward at the United States Army hospital in Armory Square in Washington. He had been present on the lawn at the White House a few evenings earlier, when Lincoln delivered what would become his final speech to a crowd celebrating the surrender of Robert E. Lee and the Army of Northern Virginia.  Booth was present on the lawn that night as well, and many historians believe he solidified his decision to kill the President that evening.

Researchers at the Lincoln Library say that in the ensuing years, Leale rarely discussed his role in the drama. Indeed, it was not until 1909, 44 years after the assassination, that he spoke publicly about the events at Ford's Theatre.

More content from msnbc.com and NBC News:

• 11 famed US sites named to annual 'most endangered places' list
• Video: Florida graduation takes explosive turn
• Prosecutors have 'bizarre' letters Sandusky wrote to victim, source tells NBC
• Coroner: Two teens killed on tracks were playing 'Ghost Train' game
• US appeals court won't revisit California's Prop 8

Follow US News on msnbc.com on Twitter and Facebook