I believe the justice system and the police are trying to play clever here. Get the CPS to lay more serious charges against Letby and have another trial. If she is found guilty then that nails shut any chance of her past convictions being retrialled. And all the protests go away.
Assuming they can find an unprejudiced group of jurors. And that there are no errors and falsehoods in the evidence presented. They will want to present a watertight case if they proceed. That’s probably why they have investigated events at a second hospital in Liverpool given the extreme criticism levelled at the Chester neonatal unit.
But if she is found innocent, then that really opens up the possibility that her first trial was unfair, with potentially biased expert witnesses and unreliable ‘statistics’, and so her convictions unsafe. This is the judges, lawyers and ministers using the system, in order not to have to make a decision themselves and not admit any possible systematic failings in the first two trials, but passing the buck onto a new jury. Most conveniently.