Rodney P. Carlisle, "Forrest, Nathan Bedford," American National Biography Online, February 2000, http://www.anb.org/articles/04/04-00389.html.
The bare facts of that attack were that 221 defenders were killed, 130 were wounded, and the remainder were captured. An uncounted number of civilians who had taken refuge in the fort were also killed. The high military casualty rate stunned the North, and rumors spread that Forrest had ordered a "Black Flag" or "no quarter," which led to the massacre of many of the African-American defenders. His troops pursued men into the woods and continued to fire on the fleeing defenders, killing many as they sought to escape. Later, Forrest's supporters and friendly biographers collected evidence from both Confederate and Union veterans of the battle to offset the conviction that he was personally responsible….
The congressional committee investigating the battle concluded that Forrest had taken advantage of a truce to reposition his forces and that he had allowed his troops to commit the slaughter. The committee heard testimony that some wounded Union troops were intentionally burned in their barracks, while other wounded were buried alive. Since Forrest was a slave trader before the war, his battle tactics were unconventional, rapid, and ruthless, and he had a personal reputation for certainty of purpose and strict discipline against any of his men charged with cowardice or violation of orders, he became a convenient symbol of the violence and sometimes explicit racism of the rebellion.