Zero 's wheelchair 's life support was turned off by Big Boss .
Big Boss kills Zero by turning off his wheelchair 's life support , and then informs Snake that the nanomachines Drebin injected into him came with a new strain of FOXDIE , engineered by the Patriot AIs to eradicate the old strains and to kill the rival Patriot faction .
Metal Gear Solid 4-COLON- Guns of the Patriots