Definition of "unnecessary"

Robins, of Torquay, had denied a single charge of causing unnecessary suffering to an animal. She claimed the microwave was accidentally turned on by one of the cats after the kitten got inside. But Knutton said the kitten was too small to even get onto the work surface.

2011 December 14, Steven Morris, “Devon woman jailed for 168 days for killing kitten in microwave”, in Guardian‎