The assassin who shot and killed former Prime Minister Abe likely used a craft-produced, muzzle-loading, double-barrel smoothbore weapon, using separate-loading ammunition which was initiated by an electric firing mechanism:
The barrels of the firearm appear to be constructed from two metal tubes (most likely commercially available pipe) that were sealed at the rear using screw-on endcaps. The barrels are attached to a piece of wood using black adhesive tape (probably electrical tape). A pistol grip is attached to the wooden body of the weapon. There may also be other fasteners which are not visible underneath the tape. Based on the general arrangement of the firearm, its design, and its apparent build quality, it is likely that the weapon was a smoothbore design — that is, the barrels were not rifled — and the ammunition was fired under relatively low pressures. The significant plumes of smoke generated when the weapon was fired indicate that it does not make use of commercial small arms ammunition propellant (‘smokeless powder’), and may instead use blackpowder or an alternative propellant. This makes the use of ‘separate-loading’ ammunition (i.e., propellant and projectile loaded separately into the weapon) more likely, as well as increasing the likelihood that the weapon was a muzzle-loading design — that is, loaded from the bore (‘front’ of the barrel), rather than the breech (‘rear’ of the barrel) of the firearm.
A popular design for simple craft-produced shotguns is the so-called ‘slam-fire shotgun’. Several observers have suggested this is the type of weapon used in the attack against Abe. However, these designs rely on conventional, impact-sensitive primers as found in modern small arms ammunition. The firing signature of the weapon suggests the use of an alternative propellant composition, as noted, and thus a slam-fire design is unlikely. The assailant likely used similar iron plumbing pipes and endcaps similar to those used on craft-produced firearms chambering conventional shotgun ammunition. However, the weapon appears to use an electric firing mechanism. Images of the firearm show that an electrical wire passes through each endcap. The trigger mechanism seems to connect these wires to two battery packs. There are several different designs of electrical firing mechanism. There have been, for example, significant developments focused on electric primers within the community of 3D-printed firearms designers. Probably the most prominent electric firing mechanism for 3D-printed firearms has been developed by the user ‘@SuckBoyTony1’. This mechanism uses an 80 kV High Voltage Pulse Generator that converts 6–12 V (the electric potential typically provided by battery packs such as that seen with the assailant’s weapon) into 80 kV. This high voltage creates a hot plasma arc between two conductive contacts that can be used to ignite flammable materials — such as propane in a grill or blackpowder in a firearm. In @SuckBoyTony1’s design, the contacts are held in place by a 3D-printed housing (see Figure 4). This igniter design can repeatedly create the hot plasma arc as long as the batteries can provide enough power and the contact rods are not worn off.
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A few hours after the shooting, Japanese police raided the assailant’s home. Following this, images of three further firearms with similar physical features emerged. One example featured five barrels, arranged in two rows (see Figure 7); the second example featured six barrels, arranged in two rows (Figure 8); and the third featured nine barrels, arranged in three rows (Figure 9). Both are wrapped in a similar black adhesive tape, and both appear to use electrical firing systems similar to that seen on the weapon used in the shooting. Improved concealability is the most likely reason for the assailant’s selection of the double-barrelled example, although reliability may also have been a factor.
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Japan has long implemented strict arms control laws. Under current Japanese law, civilians are barred from owning handguns and rifles under most circumstances, and shotguns are tightly regulated. The most recent estimate (2019) suggests that there are only 132,127 shotguns in private hands. Japan’s per capita rate of firearms ownership is the lowest amongst G7 countries, estimated at just 0.3 firearms per 100 people in 2018. As such—and in common with most craft-produced firearms users around the world—Abe’s assassin most likely made his own firearm because he could not gain access to an industrially produced example. Ammunition is also tightly regulated in Japan. Indeed, the strict control of conventional cartridges in Japan makes it more likely that the assailant selected separate-loading ammunition to avoid these legal restrictions. Reports that explosives were located at the assailant’s home may also indicate a store of loose propellant and/or a capability to produce propellant.
