Queen the deaths on the ward leapt up significantly between 2015 and 2016 and they've arrested someone.
That doesn't, in itself, prove anything. There could be a dozen reasons for the change, from pure chance to staffing changes to a bad batch of drugs.
Yes, they've arrested someone. I'm not saying she ISN'T guilty, but many many people are arrested and released. And it's a lot dicier to be sure about this stuff when your only basis for investigating is a higher rate of deaths rather than specific evidence of non-accidental harm. As I mentioned, see Lucia de Berk, who was convicted and then exonerated of multiple murders largely because more people died on her shifts than some dodgy statistics said was likely.