Andrew Bagshaw and Chris Parry were shot while evacuating civilians in the Soledar region of Ukraine a year ago.
Bagshaw’s parents, Sue and Phil Bagshaw, say evidence points to the pair being shot by the Wagner Group, the Russian-controlled private military company.
Days after their death, pictures surfaced of both men’s passports on the Wagner Group’s Telegram channel.
Phil Bagshaw said there were more witnesses he could direct authorities to.
But in a statement to RNZ, the Ministry of Trade and Foreign Affairs said that while it condemned the killings of Bagshaw and Parry, it won’t be investigating further.
“In the current situation the ICC [International Criminal Court] and Ukraine authorities are best placed to pursue any further investigation including obtaining evidence.
“For privacy reasons the Ministry of Foreign Affairs and Trade will not provide further comment about this individual consular matter including with respect to the reported causes of Andrew’s death and engagement with his family.”
The UK Foreign and Commonwealth Office told RNZ it does not investigate war crimes and also said any further investigation is for Ukrainian authorities.
Under the Geneva Convention, intentionally killing a civilian in armed conflict is a war crime.
A UK coroner’s ruling last month found Parry was fatally shot while undertaking aid work.
That differs from the initial official explanation of the men’s deaths, that their car was hit by artillery shell.
International Relations Professor Robert Patman said New Zealand and the UK could work together to investigate the death and should send a signal that it won’t turn the other cheek to war crimes.
“It’s very important, I think, that New Zealand walks the talk about upholding the rule of law, even at the time of war, and that is our official position so we need to be [as] active as we can to pursue this.”
Andrea Furger, a researcher in international criminal law and state co-operation at the University of Melbourne, said it was a standard practice for foreign law enforcement officials to travel to other countries to investigate crimes against their citizens.
Furger said this relied on the agreement of the country where the crime was committed.
Dr Marnie Lloyd, a specialist in the law of armed conflict at Victoria University of Wellington, said under international humanitarian law, countries have an obligation to help facilitate war crimes investigations, even if they did not occur in their territory.
Lloyd said if Ukrainian authorities agreed, New Zealand or UK law enforcement officials could help investigate the deaths on the ground as part of a broader ICC case against Wagner Group members.
“It’s not only about punishing the person or deterring future war crimes, but it is about documenting and witnessing what has happened.”