One thing about professionals. They are birds of a feather and they flock together. They can and do single people out for terrible things, of this magnitude? Maybe not? Would I put it past them fully? No.
As I've said before it would be a lot easier for a hospital to say there were failings and then blame one nurse who was particularly negligent. Hospitals can sue members of staff for failing to follow protocols. In order to accuse someone of murder the bar is much much higher and would require a lot more collusion and also of course being in contempt of court which is a crime. Taking civil action against a failing staff member is not completely uncommon especially if the hospital has been fined for failing and then they believe it's down to one or two individuals hence why all medical professionals need indemnity insurance. I used to be a rep for the professional union for my health profession.
Also, as mad as it sounds its actually better for a hospital to hold their hands up and say yes, there were failings, we found the staff member mainly responsible and have fired them or taken them to court, rather than saying oops we let a murderer continue working for months. Again, of course she may not be guilty but from a legal perspective for the trust using someone as a scapegoat through a murder charge does not make any sense.