"The gun that killed two Presidents" is the infamous legacy of the Kassa Fabrications Model 12 Locust. Originally created for the Systems Alliance, who wanted a lightweight weapon for high-gravity worlds, the Locust was designed to overcome the limitations of traditional submachine guns at long range.
With bullet velocity of modern weapons already pushed to the limit, the Locust's designers sought a way to improve accuracy through reducing weapon kick. They created an internal "floating bed" that absorbs the gun's recoil with minimal jarring of the gun frame itself. The barrel, magazine, chamber, and operating mechanism all move within this bed, which absorbs shock with springs and buffers. This creates a platform stable enough that the Locust can use autotargeting software usually reserved for match-grade weapons.
The Locust's lethality on shielded targets has been amply demonstrated. In 2176, a Virginian patent clerk named Michael Moser Lang brought a Locust concealed in a shoulder-mounted video camera to a photo opportunity between Enrique Aguilar, president of the United North American States, and Chinese People's Federation premier Ying Xiong. At a distance of about 25 meters, Lang pierced the kinetic barriers covering the stage with the first burst, and when Xiong heroically tackled Aguilar to remove him from the line of fire, Lang's succeeding bursts went through the premier's body and fatally wounding both men.
Donovan Hock's collection contains two antique ivory-handled Locusts, modified to take thermal clips. A detachable data drive rests in the lining of the box, containing omni-tool specifications for fabricating copies. A quick trip to the extranet reveals one of the weapons has the same serial number as Lang's original. If it's a fake, it's extremely well-made.