TDI Law Enforcement KnifeExtreme close quarters encounters where a suspect In extreme close quarters encounters where a suspect is attempting to take an officer's handgun, or an officer cannot access his handgun, the TDI knife is available as alast option knife. When worn on the pant belt the entire unit knife and sheath is well concealed. Designed by John Benner, founder and owner of Tactical Defense Institute. Now available with partially serrated blade, coyote brown handle