Why was the Lindsay Clancy trial declared a mistrial?

Lindsay Clancy's murder trial ended in a mistrial after the jury deadlocked 11-1, with jurors describing a breakdown caused by a single holdout who refused to join the majority favouring a lack-of-criminal-responsibility verdict [1, 3, 7]. The panel had actually started out more divided, initially split eight for that verdict, two for guilt, before eventually consolidating into the 11-1 split that led Judge William Sullivan to declare the mistrial [1, 4].