Detective Sergeant Derek Shaw said referring a case to the Coroner was not a step taken lightly.
But he said it was time for the family to have some closure.
"We want to extend our gratitude to all who were involved in the search for Christopher, both formally and informally, some of whom were locals and some who came from across the South Island to help."
Police still welcome any further information which may assist in finding Bates.
Shaw said anyone with substantial information should contact 105 and quote file number 180215/9929.