This incident took place in 2003 in Liberia, just across the border from Sierra Leone, where Mahony was immersed in the complex politics of the war-ravaged state. He had gone to neighbouring Liberia at the end of warlord Charles Taylor's rule, where Taylor's rivals were stitching up new political coalitions.
Nearly 10 years on, Taylor, Sierra Leone and Liberia are back in focus and Mahony is again plugged into events, though now as an authority on justice and human rights in a troubled region where thousands have died in vicious conflicts.
Today Mahony is deputy director of Auckland University Law School's newly created New Zealand Centre for Human Rights Law, Policy and Practice. He will also teach parts of the international human rights and international criminal law papers, while he finishes a doctorate through the University of Oxford.
Last week, as many cheered the war crimes conviction of Taylor, claiming it sent a signal to tyrants that their days of impunity were numbered, Mahony took a different view. Victor's justice, he called it, with one guilty man convicted while other culpable figures remained off-limits to prosecutors.
Such as? Mahony considers the late Libyan dictator Muammar Gaddafi and Burkina Faso President Blaise Compaore just as guilty of the ghastly crimes levelled against Taylor, who armed Sierra Leone rebels in return for so-called blood diamonds mined by slave labourers and smuggled across the border.
Another to get off scot-free was Sierra Leone's then-President and Defence Minister, Ahmed Tejan Kabbah, who is alleged to have supported a militia that also committed a catalogue of war crimes.
The reasons these abusive figures went untouched, argues Mahony, has everything to do with an international justice system that reflects global power, rather than global justice. Deals were cut and funding threats made that meant the court did not touch some of the most powerful criminals.
In Taylor's case, his demise largely reflected a change in United States foreign policy. Extraordinary though it may seem, Taylor previously enjoyed strong backing from the Clinton Administration. Support in the US was led by the then-US Special Envoy for Human Rights and Democracy in Africa, Reverend Jesse Jackson. Taylor had another friend at court in the late Congressional Black Caucus leader Donald Payne.
Britain, the former colonial power, backed Kabbah and had armed his militia.
Then US policy changed, and Washington helped create a special war crimes court to indict its one-time ally Taylor.
Mahony has been close to these events, from his time in Sierra Leone, and from work with institutions trying to create a better future for the small West African nation.
SO HOW did the former King's College pupil get to Sierra Leone? He had returned to Auckland for the 2002-2003 summer from studies at Otago University. A friend put in him in touch with David Shearer, who back then was home from his United Nations job. As Mahony helped the future Labour leader paint his North Shore house, they talked about Shearer's human rights work in Africa.
Shearer convinced Mahony's parents in Parnell that Sierra Leone, which had emerged from its devastating 10-year civil war, was safe for a raw young man from New Zealand.
Initially Mahony did fieldwork for a project Shearer had started called the Campaign for Good Governance. Then he got on board Sierra Leone's Truth and Reconciliation Commission, set up to investigate the horrific conflict.
His job included taking statements from victims of the bloody civil war, which is blamed for tens of thousands of deaths, widespread rape, the deployment of child soldiers and the signature crime of amputation.
The law student heard "many horrible stories. Kids being forced to kill and rape their parents or siblings, unborn babies being cut out of pregnant women, all sorts of horrible acts of torture."
At weekends he spent time at a hostel teaching English to children orphaned by the war. Over time they told their stories and how they had reached the hostel, living on insects and begging for food as they crossed the countryside.
Mahony recalled that when he went to leave, the children would ask if it was going to be okay for them because they had learned some English. He tried to say yes, but they could read a different story in his eyes.
Though still some way off completing his legal studies, Mahony wrote a section on governance in the commission's's final report and had a hand in a chapter on the factors that drove Sierra Leone to war.
He says the report remains a reference work for aid groups and other institutions.
"I was in effect a fortunate victim of circumstances," he says, as he got the writing job because there was no money to hire the sort of high-powered lawyer who would normally do the work.
"I was a 21-year-old kid who'd gone there and done interviews, and it just so happens that more out of ignorance to the political sensitivities than anything else was willing to publish something about corruption in Sierra Leone and some of its systemic drivers."
Mahony returned to Sierra Leone and Africa in 2008, at the request of the UN-backed Special Court for Sierra Leone to direct the design of a witness protection programme. The work expanded into a book, Witness Protection in Africa. By this time, Mahony's rugby career was steaming along as a member of the Auckland NPC squad.
To keep fit, he practised in the early morning at the main stadium in the capital Freetown with the national athletics team.
The special court took nearly six years - at a cost of US$250 million ($312.2 million) - to convict Taylor. Mahony is reluctant to weigh up the impact of the verdict on the people of Sierra Leone, saying it would be condescending to suggest how individuals might respond. But he firmly believes the court's verdict means heads of state who support crimes are fair game - as long as the world's great powers agree their time is up.
They decide, says Mahony, who is - and who isn't - put in the dock.
See also
Chris Mahony in The Atlantic Online
http://tiny.cc/5fwpdw and in a new book, http://tiny.cc/nudrdw
