They will be tried under the UCMJ, AFTER they are tried by civilian authorities. They can be convicted and sentenced separately for both without violating double jeopardy, since violation of UCMJ is actually a separate federal offense, as opposed to the state offense of murder.
Exactly, doc. The great thing about it is that the ones most directly involved will be sitting in stir for a year before the case even comes up for arraignment under the civilian system, depending on whether they can make bail (Which is prohibitively high in most death cases for the principal actors), and the much-shorter clock on the military trial won't start to run until the military gets them back and formally charges them.