The text on the web page is the script of the cable television show about the Patapsco Guard, developed by the Howard County Genealogical Society. 

Since that date, additional information about the circumstances surrounding the death of John T. Redman have come to light.

First Source

Here is the full newspaper article on the murder.  Source: Kittochtinny Historical Society, Chambersburg, PA  It has no date except Dec. 1864.

SOLDIER SHOT ~ on Saturday night last a melancholy affair took place at a German drinking saloon on East Market Street which resulted in the death of John Redman, a member of the Patapsco Guard, now doing provost duty in our town.   The circumstances are about as follows.  

Redman and several others were in the saloon playing dominoes, when Lieut. Underhill, post Provost Marshall, and finding they were out without passes, ordered them back to camp.   The men fled out of the back door to get away from the Lieut. who ordered them to halt.   They did not obey the order and he fired four times after them, two of the balls entering Redman, one in the back and lodging in his bowels, causing death in a short time.  

A post mortem examination was made by Dr's Suesseroff and Montgomery, and a coroner's inquest held by Esquire Hammen which rendered a verdict in accordance with the foregoing facts---Lieut. Underhill is under military arrest and will be tried by court martial.

Second Source

Another interesting piece of information was provided by the men who are writing the book on the 1st New York Artillery, Battery A.   While researching material for their book, they came upon several letters written by the men in Underhill's company.  
A soldier who was in Underhill's company wrote a letter telling his father a story of a battle in which Lt. Underhill ordered the men to unhitch the horse from one of the caissons, upon which Underhill rode the horse to the rear of the line and proceeded to hide behind a boulder until the fighting ended. 

The soldier told his father that the army must sure be hard up for soldiers if they picked a man a cowardly as Underhill.  (This is an indirect quote; we do not have the exact text of the soldier's letter.)
Third Source

Relatives of  John T. Redman have researched the military career of Lt. Underhill at the National Archives, and their findings cast an interesting light on this incident.  According to Redman family tradition, a drunken sergeant confronted Pvt. Redman in a barbershop and demanded that Redman salute him.  Before Redman could respond, the story goes, the sergeant shot and killed him.

Here is what was uncovered at the Archives:

1. A charge was leveled against Underhill for theft. A civilian had brought his horse (with saddle) to the camp where Underhill was assigned. When the civilian went to get his horse, the saddle had disappeared. When a search of the camp was made, it was found that Underhill had stolen it.

2. He was court martialed on April 21, 1864, for the charge of "violation of the 5th article of War" for an event that happened in October of 1863. Specifically, the charge was as follows "...the said Lt. Edward H. Underhill, Battery A, 1st New York Artillery, did use contemptuous and disrespectable words against the President of the United States and against the government of the United States using the following words:    'I hold no commission under this damned Lincoln-nigger government or administration. I hold my commission from Gov. Seymour (democrat, New York) who is a gentlemen.' This at Pottsville, Pa. on or about the 10th day of October 1863."

Underhill (whose home state was New York) was found guilty and the court sentenced him "to be dismissed from the service of the United States".  "The proceedings...were approved by the Major General commanding and the record forwarded to Washington."..."The President directs that the sentence be commuted to 'loss of pay proper for six months' by the Order of the Secretary of War."

3. On January 11, 1865, Lt. Underhill was charged with "murder with malice aforethought" in connection with the shooting of John T. Redman. Court Martial dropped the "malice aforethought" part of the charge, but tried him for "murder". Underhill pled "not guilty". The court martial found Underhill not guilty of murder, but did find him guilty of man-slauqhter. His sentence was "to be dismissed from the service of the United States with loss of all pay and allowances since Dec. 3, 1864 (which was the date he shot John Redman); he was to be imprisoned for the period of two years...he was to pay a fine of $250 and stand committed (to prison) until the fine is paid in full."

But the fine and imprisonment were commuted.

4. "The proceedings findings and sentence of the Commission in the case of .Underhill were approved by the proper commander and the record forwarded for the action of the President of the United States. The findings and sentence are disapproved and Lt. Underhill will be restored to duty. By order of the Secretary of War."

Fourth source
Other descendants of John T. Redman provided more information.  He was married to Anna Mary Holland (Redman, Culler) Movember 15, 1863.  Anna Mary and John had a son, John William Redman, who was born on June 21, 1864.   After the death of her husband, Anna Mary tried unsuccessfully to obtain a pension for her son John William.  With each application she was repeatedly denied.  She never gave up her appeals for a pension and continued her quest up to her death in 1942.
Lt. Edward Underhill was never made to serve his punishment or pay the fine ordered at his court martial.    He was actually restored to duty.  He was from a very prominent family in New York and his family connections kept him from punishment.   Two men who are trying to collect data on the men who served in the 1st Light Artillery were puzzled at Lt. Underhill's constant movement from one regiment to another.   It seems that nobody really wanted him in their company and he was constantly being transferred from one company to another.  
There was no information on the location of his burial in his pension papers.