The Department of Conservation (DoC) has identified members of a Norwegian hunting party shown in an internet video with protected New Zealand birds they allegedly shot.
However, it says charges cannot be laid in this country, because they have returned home.
It says it has passed their details to authorities in Norway, but the police there say it is not possible to launch a prosecution.
DoC says the Norwegian police could lay charges only if the birds were on the verge of extinction, and kereru are not endangered enough.
The video was posted on You Tube last week showing the group of five men posing with a pair of dead kereru, or wood pigeon. They are also shown holding up dead tahr, wallabies and a paradise shelduck.
The kereru, New Zealand's only native pigeon, has been fully protected from hunting since 1922, even though it is no longer classified as threatened. Paradise ducks are only allowed to be hunted in season.
DoC says the footage seems to show the group hunting in the Whataroa Valley near Franz Josef on the South Island West Coast in January.
The department's wildlife enforcement group worked with the Customs Service and police on the investigation.
DoC has cleared the helicopter pilot who transported the group of responsibility.
Other wildlife cases
It is the third public case this year involving European tourists. In two separate cases, Germans were jailed for more three months each for trying to smuggle native lizards out of New Zealand in their backpack and underpants.
DoC says the maximum penalty for killing absolutely protected wildlife such as kereru is a $100,000 fine and up to one year's jail.
Conservation Minister Kate Wilkinson says her department is looking at ways to toughen penalties to stop foreigners found guilty of such offences from ever coming back to New Zealand.
The Norwegian National Authority for Investigation and Prosecution of Economic and Environmental Crime says it is possible to prosecute their citizens for some hunting crimes committed overseas.
The authority's police prosecutor, Aud Slettemoen, told Morning Report there is a high bar for prosecution.
She says the species needs to be threatened by extinction and the hunt proven to have reduced its population.
