Katana

A katana is a single-edged, curved Japanese sword typically associated with Samurai. It is roughly 60 inches long, and has a long handle to accommodate a two-handed grip. Katanas are known for their sharpness and are able to sever limbs, including heads, in a single strike. It's hardness is attributed to the steel, which is folded and re-hammered over 200 times. The curve of the blade is achieved through the use of differential quenching; that is, a layer of clay is painted on the back half of the blade to insulate it. The blade is then heated and quenched. The two different temperatures of the front (bladed) side and the back (flat) edge cause the blade to curve as it is cooled at different speeds. This ensures that the curve is almost perfect in formation, as opposed to manually curving the blade during forging; as is the case with other types of swords.

Criminal Minds
Johnny McHale owned a katana and it is believed that he used it to kill his victims; though he imagined himself as having used two scimitars like his comic book character.