It has to do with an incompetent State AG trying to be relevant by Nifonging a physician and two nurses.
Can the state indict no murderer if it is unable to apprehend and indict all murderers?"
The state can indict as many people as it wants for any crime they want (see "ham sammich"). They can also misallocate the limited investigative and prosecutorial resources all they want as well. That doesn' make it morally right, even if it is politically expedient.
We obviously differ on the morality of these particular murders.