Both of the stories you mentioned in the post are substantially true. In April 1863 a member of the 4th U.S. Cavalry murdered Capt. Samuel L. Freeman after his capture near Franklin TN. Near Selma AL on the evening of April 2, 1865, Forrest and his escort came upon a party of men from the 4th U.S. Cavalry under command of Lieut. Elbridge G. Roys, General Wilson's chief of scouts. Elbridge and several other Federal troopers were killed, the Confederates suffering no losses in this encounter. Both incidents are carefully described by Forrest's biographers.

http://www.civilwarnews.com/archive/articles/shiloh_relic_hunt.htm

There is a marker in the Camden cemetery for Lieut. Joshua Holt, killed Apr. 23, 1865. Most people interpret the word 'died' to mean that death occured as a result of military action, which is often not true. However, the marker clearly reads 'killed', which tells us that some form of violence caused Lieut. Holt's death.

Something else to consider -- on April 23, 1865, there were no Federal troops anywhere near Camden. The nearest U.S. soldiers could be found at Greenville, roughly thirty-five miles east. Furthermore, Federal reports make no mention of meeting any resistance during General Smith's march north towards Montgomery.

Another of Forrest's officers, Capt. Addison Harvey, was killed on April 19, 1965. According to the Official Records, Capt. Harvey was assasinated while attempting to restore order in the streets of Columbus GA. This took place during the rioting which began after Wilson's cavalry command left the city. [Note the last paragraph in this article.]
http://theusgenweb.org/ms/madison/harveyscouts/honors.htm

We spend little time studying these kinds of events, since they essentially involve law-and-order rather than military events, but quite a number of Confederates were killed -- murdered might be the best term -- as the war was ending. Lieutenant Holt might have been one of them. He could have been attempting to protect Confederate stores or a private home. He may have been attempting to arrest a deserter or enroll a conscript. We just don't know enought to say for sure.