If a person committed (or is suspected of...) multiple Federal felonies, and one of those is much simpler, quicker, clear-cut, more straightforward AND less likely to generate a collective media/public paroxsysm, months of premature speculation and criticism, and heightened anxiety for a fugitive of unknown mental stamina and fortitude...seems like a good idea to go with that one first. The case is well-known enough that getting attention and resources wouldn't be harmed by going with a less sensational charge at first; everyone knows he is, formally or informally, the most likely suspect and most likely with the most informations, and merely having a Federal warrant in place was enough to support various LE cooperation, etc. It's really common for prosecutors to start like this. It's a strategy appropriate for many situations. In this case, too, where facts and theories of the case are still relatively early in development, it would be a mistake to select a degree or type of homicide (or other crime) to charge without knowing more. You don't want to have to keep amending/going back to the grand jury. That irritates everyone, among other potentially bad consequences. If you have a situation where some guy, fresh off 25 years of hard time, is caught on camera point-blank shooting bank tellers in the head while robbing the bank of a million dollars and then car jacking a little old lady, snatching her purse, shooting her and her cat, and then running over a pregnant lady pushing a baby carriage and barreling through a crowd of disabled orphans as he flees the scene, you might go out with a murder indictment early and not focus on the fact that he next stopped by the 7-11 and bought three slurpees with her credit card. Because in that situation there's not necessarily a lot of grey area as far as facts specifically needed to fit statutory language - hard to imagine a reasonable scenario that ends in "he didn't do it.". Plus, in that case, you've got a known dangerous element out there, so "wanted for murder" is also a public safety warning about someone known to kill with reckless abandon.