Can rhinos cure cancer?
They emerged with a small consignment of ivory and rhino horn worth an estimated 850,000 rand - about £75,000, or $114,000.
The rhino horn - which came from animals that had died naturally - was probably destined for Vietnam, where the popular folk tale about its capacity to boost powers in the bedroom has been augmented by a belief that it can cure cancer.
Last year, a Vietnamese diplomat was recalled to Hanoi after being filmed apparently buying rhino horn outside her embassy in Pretoria.
The Addo Park hold-up is perhaps the most striking event to date in what is, by all measures, an escalation in the illegal wildlife trade.
Put together a dwindling resource (in some important species, at any rate) with a growing demand and capacity to pay, and there is only one outcome.
It's a trend that has just been raised at the Convention on International Trade in Endangered Species (CITES) meeting in Doha, Qatar, where UN agencies have warned again about the urgent plight of the tiger.
Across all sub-species, only about 3,200 remain in the wild. That is considerably fewer than exist in captivity - in the farms and breeding centres of East Asia, and in zoos across the world.
Forgive me if you've heard it before, but to me it is still a staggering statistic that if you were to pick a tiger on the face of the earth at random, the odds are that you would be picking one born and bred in captivity.
Wild tigers now exist mainly in small, fragmented populations - a pattern that promotes lack of genetic diversity and hence is often a step on the road to extinction.
Whereas some governments have stepped up to the plate, all the links in the chain that the wildlife gangsters need appear to be functioning well enough.
I had a chat with John Sellar, who heads CITES's enforcement operation.
"It's now four decades since we realised the tiger was in trouble," he noted.
"We've spent millions of dollars on it and we have failed miserably - I like to be optimistic but we have to ask ourselves whether we are really committed."
In south-east Asian countries, he said there was now evidence of a demand for tiger meat.
As a former policeman, he said he found the situation incredible.
Conservation organisations are routinely finding evidence of abuse, of poaching and illegal trading - and many police forces and customs authorities just aren't acting on it, as one presumes they would if the cargoes contained heroin or AK-47s.
As to the price of rhino horn in one of Hanoi's unlicensed (and ineffective) "cancer clinics", Mr Sellar would not be drawn, suggesting that the information could encourage further poaching.
The black rhino, by the way, is already listed as critically endangered.
Often we envisage the solution to environmental problems as being about laws and policies, or markets and incentives, or scientific research and public awareness.
Here is an equation far simpler.
Unless police and customs forces stop the gangsters involved in this business, there will be no more tigers and no more black rhinos in the wild: that's it.