To answer boxmover's question, the vast majority of civilian pilots in the US use Jepps.
I checked out the Kirksville plate yesterday and found it far easier to read than the NOS plate shown here.
One possibility is that considering that the pilot reported the field in sight shortly before impact and the MDA is 356 ft and can be reached quite easily 2 to 3 miles out from the threshold using a non precision descent rate, is that the pilot had visual and then commenced a visual descent at 300 ft/nm in "Black hole" conditions which would have impacted the ground 1 or 2 miles short of the threshold.