Definition of "trusty"

We usta have a rule that if a trusty shot an escaping convict, then the trusty would go free.

1941, James Howell Street, In my father's house

The cell block is clean and doesn't smell of disinfectant. The trusties do all the work. The supply of trusties is always ample.

1953, Raymond Chandler, The Long Goodbye, Penguin, published 2010, page 58