Elias Fall's a negro soldier testified at the Congressional Committee that General Forrest expressly gave orders to stop shooting, and that, "after peace was made," an office told a "Secesh soldier," if he did that again (shoot), he would arrest him.
The burned bodies you refer to probably came from the Federals burning the fort or the New Era gunboat shelling the Confederates as they buried Union soldiers following the battle.
Thomas Addison's testimony was unreliable as well.
Also if you look at the questioning of the committee, the questions were phrased in a leading fashion.
Here is what the Memphis Argus (Memphis was in Federal hands at the time) said of the Fort Pillow battle as reported in the New Orleans Daily Picayune (New Orleans was also under Federal rule):
Capt. Young, Provost Marshall, was taken prisoner, slightly wounded, and paroled the liberty of their camps, and allowed to see his wife. He says that our troops [the Federals] behaved gallantly throughout the whole action, that our loss [Federals again] in killed will exceed 200; he also stated that Gen. Forrest shot one of his own men for refusing quarters to our men.
IIRC, there are a couple of documented occasions where Forrest personally shot one of his own soldiers in the heat of battle for not following his orders. You didn't want to encounter his temper.
Forrest also would threaten the enemy with annihilation if they didn't surrender. Here is what Union correspondence said Forrest sent them at the Battle of Murfreesborough:
MURFREESBOROUGH, July 13, 1862.
COLONEL: I must demand an unconditional surrender of your force as prisoners of war or I will have every man put to the sword. You are aware of the overpowering force I have at my command, and this demand is made to prevent the effusion of blood.
I am, colonel, very respectfully, your obedient servant,
N. B. FORREST,
Brigadier-General of Cavalry, C. S. Army.
The threat often worked. Forrest was known to treat prisoners fairly.
Forrest had a strong advantage at Fort Pillow which he pointed out to the Feds. He sent them a surrender offer twice. The Union soldiers in Fort Pillow were holding out for reinforcements from visible Federal boats on the Mississippi and didn't accept Forrest's offers. Forrest sent part of his force down to the river to successfully block the Union reinforcements.