J.
To get rid of the smell, completely wet the mattress top with Nature's Miracle (available in pet stores.) Then allow to dry - you may need to either flip the mattress or have him sleep in another bed to give it time to dry, because you really have to drench it.
I didn't really notice a stain - not sure if the NM got rid of it, or if we have just been lucky. But Oxyclean is great at all biological-type stains, maybe you could try spraying that on (after the NM treatment is dry.)