While innocent people have been found guilty in the past. I have yet to hear of a serial killer being proved innocent. Often it is rather that they have only been convicted of a few of their crimes and there is insufficient evidence to convict them of more. For example the police know who killed Suzy Lamplugh. He is a man serving a prison sentence for several killings, but they lack sufficient evidence to able to ensure a conviction.
Nurses, by very definition, are going to have to be very subtle in the methods and times they use to kill their patients, making proving their guilt very difficult.
The three most recent nurse serial killers, Beverley Allitt, Ben Geen and Colin Norris, all acted much as Letby did, in how they killed or injured their victims and the circumstances in which they did it..
Recently further investigations into Letby's nursing history suggest that her potential victims extend well beyond those for which she was tried for.
Lucy Letby has been convicted of seven murders and seven attempted murders, and there were other cases where the evidence was not strong enough for presnentation to the court. It beggars belief that someone innocent of any crime at all could be misconvicted on a total of 14 different cases. across 2 seperate trials, with suspicions that she could have been involved in probably another 14, at least, cases, across several hospitals.