Saw

A bit of a puzzler...
A wee bit of human bone was found in an old pipe trench in a churchyard. Not surprising, you would think. Only it was a left arm of an adult (probably a woman) and the right arm of a 16 year old, probably a boy.
Hmmm
And both had been sawn off just below the shoulder.
Hmmm

There was a hospital close by.
Aaaaah...