Under Islam, apostates may be killed, even if they are nominally Muslim. Good Muslims are not supposed to kill other good Muslims under any circumstance.
That said,
What we would call a 'moderate Muslim' is an apostate. Rejecting jihad, living peacefully with your infidel neighbors and friends, pretty much anything that's not fundamentalist Islam, can be construed to be apostasy. That means that under Islam, it's more permissable for Bin Laden to kill American Muslims than it would be for them to kill him.
My tagline is also instructive on this issue.
The same as a "Good German" back in WWII.