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The family's hopes were raised at the weekend when a tracker dog picked up his scent after first smelling Louie's blanket.

More than 40 State Emergency Service volunteers, WA police, park ranges and the tracker dog team had combed the area since Thursday.

He had always been the scout, the tracker dog.

The sensitivity of a trained tracker dog might be hard for humans to match.

The police in Zurich, the largest city in Switzerland, used tracker dog units to hunt the gunman.