Vesper killed his artist as a demonstration to Takeshi as to what will happen to him if he doesn't secure those XCOM perms. He still hasn't, and that's why he's still on the run, and why Vesper has arranged his space so that he can strike the door with his spear without having to leave bed, just so he can be ready to unleash the Gae Bolg at a moments notice in case a Takeshinobi creeps into his apartment and makes it past his security system (it's his speargun aimed at the door with a tripwire trigger).