I can/could kill you

[99bottles]

Generally, I know the difference between can and could, but in this sentence, I'm not sure which I should use.

I can/could kill you right now, but you deserve to suffer first.

 

[Tarheel]

I can't think of a reason to use can. Also, with could it seems like a threat. (What else could it be?)

 

[Tdol]

I could suggests that the person is prepared to kill. I can would suggest that they have permissions to kill. From movies, the first is far more likely.