A search of the online newspaper database at the Australian National Archives turns up only one mention of Mitta Mitta Jack. The name, however, is given as Ahrens, not Ahern.
From The Argus (Melbourne, Victoria) 29 March 1871 The Ovens Advertiser thus notices a case of suspected murder:-"Search has been made during the past week by the Albury police for the remains of a man named Griffiths-formerly a mate of the famous, or rather infamous, Mitta Mitta Jack-who suddenly disappeared some l8 years since, and was never again heard of. It has long been suspected that Griffiths came to a violent end, and apparently the police are in possession of some fresh information on the subject, as we are informed that during the present week they were engaged in searching the wells at the rear of the old Criterion Hotel and in other parts of Albury. It is said that the term of imprisonment to which Ahrens [sic]-or Mitta Mitta Jack, as he is more generally styled was sentenced will soon come to an end, and that he may soon be expected back to his old haunts, ready for a fresh career of villany and crime."