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Detective Sergeant Chris Henderson said he was unable to go into specifics, but "we will advise the victim and then the public when an arrest is made''.
The horse, Star, died from its wounds after the attack, prompting an outpouring of concern in the township.
Det Sgt Henderson said the investigation into the killing was ongoing.
"Police are taking this matter very seriously and Crime Squad 3 continue to manage the case.''
Anyone with information was asked to contact Crime Squad on (03) 471 4800, or Crimestoppers on 0800 555 111.