Tueller has said in video interviews that he never designed nor presented his firearms training drill as an organized, outlined, and implemented research project involving the applied sciences of psychophysiology, physics, and related human factors. No forensic testing, examination, reconciliation of data, or scientific oversight of a research model was ever conducted.
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Actually, there are no forensically proven facts that I am aware of that specifically verify or conclusively establish that a suspect armed with an edged weapon will more likely than not be able to seriously injure or kill an officer armed with a sidearm on all occasions and circumstances. The truth is that the 21-Foot Rule should not be considered to be an absolute rule at all because there are too many variables involved at this point to call it a "rule." Let's discuss them.