A higher dose affects coordination and makes the heart throb. Then comes collapse and death. Often the victim is unaware and just drifts slowly to sleep. Blood is fluid and doesn't want to clot. Lungs congested and the upper air passages contain a frothy fliud.
Carbon monoxide remains in the blood for up to six months after death.
As with most acids, not usually used to kill someone, but can be used to dispose of the corpse afterwards. Corrosive and colourless. Nitric Usually colourless, though goes brown when oxidised. A dehydrating agent that extracts water from the body. Is strong enough to eat through bones as well as flesh.