The very basis of the fact there are any murders at all rests, it seems, primarily upon this man's opinion (I think one other doctor was mentioned in the opening remarks, but primarily it was Dr Evans) discredit him and there isn't even a crime to answer for.
The other main aspect will be how they selected which crashes on the ward were intentional and which were routine. The defence will no doubt argue that a crash where LL wasn't present was considered routine, but a crash where she was present was considered intentional, they only need to find one crash where she wasn't present, sufficiently similar to the ones for which she is charged so they can say "Look, they cherry picked crashes where she was present for the charges.