In February 2017, officials at The Countess of Chester Hospital in England's north began probing an alarming increase in unexplained deaths and near-deaths on its neonatal ward.
The region's most high-needs babies were diverted to other hospitals as a precaution, and an independent clinical review was launched, which uncovered procedural issues and "significant gaps" in staffing.
By that May, focus narrowed to one staff member in particular: a nurse named Lucy Letby.
On Wednesday, after a lengthy investigation involving multiple arrests, the 30-year-old was charged with eight counts of murder and another 10 of attempted murder relating to infant patients at the hospital.
Here's how the case has unfolded.
Who is Lucy Letby?
Lucy Letby had first worked at the neonatal unit of The Countess of Chester as a student nurse, before graduating from the University of Chester in 2011 with a degree in child nursing.
She performed a placement at Liverpool Women’s Hospital as part of additional training in neonatal intensive care, but worked primarily at The Countess.