Qualified Privilege would apply - it's their duty to give information.
Secondly, there was a defamation case where if I remember correctly a newspaper stated police held some man for questioning. He sued the newspaper because he said he was defamed by the implication of guilt. It was held that as the outcome of questioning was not necessarily being put in jail, a right thinking member of society would not assume he was guilty.
(The test for defamation is "does it reduce the standing of the individual in the eyes of right thinking members of society").
Also of note is: the test for defamation is a civil test "on the balance of probabilities", whereas criminal cases are "beyond all reasonable doubt". So despite the fact that someone is acquited, it does not mean they'll win in the civil court. (As in the O.J. Simpson case).
Secondly, people with criminal records can't fall very far in the eyes of right thinking members of society, so even if there is defamation, they won't be entitled to much damages.