The Collaborative International Dictionary of English v.0.48:

Rogatory \Rog"a*to*ry\, a. [See Rogation.]
   Seeking information; authorized to examine witnesses or
   ascertain facts; as, a rogatory commission. --Woolsey.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

ROGATORY, LETTERS. A kind of commission from a judge authorizing and
requesting a judge of another jurisdiction to examine a witness. Vide
Letters Rogatory.