For the past decade, poachers have killed rhinoceroses in the wild and in protected reserves around the world at alarming rates, threatening the survival of four of the world's five rhino species.
The poaching is driven by a demand for rhino horns in southeast Asia that has grown nearly insatiable; so much so, experts say, that any living rhino - anywhere in the world - is now at risk of being killed.
Perhaps no rhino death illustrates that threat more forcefully than the killing of Vince, a 4-year-old male white rhino who was slaughtered this week inside his enclosure at a zoo outside Paris. The rhino - discovered by his keeper at the Thoiry Zoological Park today - now holds the ominous distinction of likely being the first rhino to be killed by poachers inside a zoo, experts said.
"This is the first time we've heard of it," said Crawford Allen, senior director of Traffic North America, a regional office of the World Wildlife Fund (WWF). "It's certainly the first time it's happened in Europe.
"It's an incredibly shocking and distressing occurrence," he added. "It's also a game-changer for zoos. They've woken up today and realised their world has changed if they have live rhinos in their collection."
In a statement posted on Facebook, the Thoiry Zoological Park, which is 50km west of Paris, said its "entire staff is extremely shocked" by Vince's killing. The animal was born in a zoo in the Netherlands in 2012 and arrived at Thoiry in March 2015, the zoo said.
The zoo pinned the killing on criminals who forced open an outer gate outside the rhinoceros building overnight. The intruders then forced open a second metal door and broke open "an intermediate inner door" that allowed them access to the animal lodges, the zoo said.
Police told Reuters that Vince was shot three times in the head. One of the animal's horns was removed, probably with a chain saw, the zoo said.
"His second horn was only partially cut, which suggests that the criminals were disturbed or that their equipment proved defective," the zoo said. "The other two white rhinoceros living in Thoiry, Gracie, 37, and Bruno, 5, escaped the massacre and are safe."
"Vince was found this morning by [his] caretaker, who is very attached to the animals she cares for, and is deeply affected," the zoo added. "This odious act was perpetrated despite the presence of five members of the zoological staff living on the spot and surveillance cameras."
Just over a decade ago, a rhino horn was just a rhino horn - an innocuous piece of animal body armour made of keratin, the same type of protein that makes up human hair and fingernails. Now a rhino horn is something else entirely for a new generation of wealthy buyers in China and Vietnam: a highly-coveted status symbol and a cancer-curing miracle drug and aphrodisiac whose legend is rooted in pseudoscience.
Depending on the species and the market, experts said, rhino horns are worth more than their weight in gold. Protected wildlife is the fourth largest form of criminal traffic in the world behind drugs, counterfeiting and human trafficking, according to the World Wildlife Fund.
Global trade in rhino horn is banned by a UN convention, and its sale is illegal in France, according to Reuters, but as little as a kilo of rhino horn was worth about US$54,000 on the black market in 2015.
By the early 1990s, the southern white rhino population plummeted to a few as 50 animals left in the wild, according to the conservation group Save the Rhino. The group said the animals' numbers have increased to about 20,000 after conservation efforts, but those numbers are once again falling due to a new wave of poaching since 2008.
According to new data published by the government of South Africa, 1054 rhinos were poached in 2016. That number is down from a year earlier, when 1175 rhinos were poached, a 10.3 per cent decline. There have been more than 1000 rhinos poached in South Africa for four consecutive years, the WWF notes.
"For 2016 there were a staggering 2883 instances of poaching-related activities (such as poaching camps, contacts, crossings, sightings, tracks and shots fired) in the park, compared to 2466 recorded in the same period in 2015," the South African Government reported.
"This is an increase of 16.9 per cent. These criminal gangs are armed to the teeth, well-funded and part of transnational syndicates [that] will stop at nothing to get their hands on rhino horn."
Experts said the skyrocketing value of the horns led wildlife conservationists to begin warning several years ago about the likelihood of captive rhinos being targeted by poachers. The warning signs, they said, came in the form of a spate of rhino horn thefts from private collections and exhibitions.
With rhino killings increasing dramatically and private collections under threat, many experts decided it was "only a matter of time" before a killing inside a zoo occurred.
Today, the warnings became all too real.
"I wish I was surprised, but these animals are so brutally targeted," said Cece Sieffert, deputy director at the International Rhino Foundation, which supports rhino conservation in African and Asia.
"Wildlife crime is run by organised crime syndicates with very complex networks of middlemen moving rhino horns from Africa and India to networks in Southeast Asia. With the poaching crisis at such an alarming rate, it was sadly only a matter of time before these animals in zoos and other protected areas were targeted."
"It's absolutely heartbreaking for the keepers who devote their lives to taking care of these incredible animals," she added.
While the idea of killing a rhino inside a zoo may sound more daunting than selling heroin, Allen said that's not necessarily the way criminal gangs see things.
"It's really a no-brainer for these criminal groups," he said. "It's a low-risk, high-profit enterprise for them, and they can make as much money robbing a bank as they can killing a rhino with far, far less security."
The attack in France comes two weeks after two armed men stormed a rhino orphanage in South Africa, according to the Dodo. The men assaulted members of the staff before holding the group hostage and killing two baby rhinos for their horns, according to a statement posted on Facebook by the Thula Thula Rhino Orphanage.
Suzie Ellis, executive director of International Rhino Fund, said the boldness of the latest attacks - which follows museums and private collections being targeted - is a sign that "zoological facilities need to take serious measures to keep their rhinos safe."
Allen said zoos need to do risk assessments as soon as possible. He also recommended upgrading security equipment to include thermal imaging cameras that can automatically identify humans, as well as hiring more security guards.
"The people who targeted the zoo in France have probably already checked out other zoos that they can target," he said. "Unfortunately, it sometimes takes a horrific wake-up call for things to change."