Isn't it more 'if he's prepared to kill himself, then he's prepared to kill us'? You could say that it's future reference as the killing would have to be after the time of speaking, but I wouldn't say that the modal is there to indcate futurity. Apart from assumptions about completed actions in British English, there's almost always a degree of futurity there when 'will' is used, even when telling people that you'll answer the phone. However, I think there's clearly something else at work in this sentence; I don't think the speaker is informing me simply about some possible future event, but trying to get inside the head of the nutter.
With will..will conditionals, there has to be more than simple futurity, otherwise they'd just follow the pattern of a regular first conditional:
If you do the dinner, Metal, I'll do the washing-up.
If you'll do the dinner, Metal, I'll do the washing-up.
In the second sentence, the actions are in the future, but that's not why I shoved the 'will' in the first part. I put it there to balance the two halves, and to try topersuade you to put on an apron and get busy in the kitchen.
I could have left the first 'will' out without affecting the time frame at all. I presume Mr Grsham's sentence has a similar function.
But then, I've never believed that English has a future tense, or that 'will' functions only to indicate future time.
