JOHANNESBURG - It was after the second or third corpse was found that conservationists at the Pilanesberg game reserve realized they had a major problem: Someone, or something, was systematically killing rhinos, and the chief suspects were elephants.
Elephants don't normally kill rhinoceroses. So when the attacks began in April, the game rangers on the reserve, north of Johannesburg, were reluctant to believe what was happening.
But the evidence, although baffling, was unmistakable.
Some of the dead rhinos had gaping wounds, shaped like elephant tusks, in their backs. Others had suffered broken ribs and internal injuries that could have been inflicted only by a much larger animal.
There were upturned and trampled trees at the death scenes - always a telltale sign of elephants. And finally, the giveaway of many a murder mystery, there were footprints - elephant footprints.
By June, the serial elephant killer or killers had claimed four confirmed rhino victims and six suspected ones whose corpses were too badly decayed to establish positively the cause of death.
But Greg Stuart-Hill, the region's chief ecologist, said there are few doubts that the six also had fallen prey to the same killers. The reserve normally registers one rhino death, of natural causes, every two or three months.
Ten died in just three months this spring, and five were wounded. In addition, two orphaned baby rhinos died as an indirect result of losing their mothers; one was ravaged by lions as it tried to defend its mother's body.
For the park's management, it was a nightmare. Ecological thinking these days favors allowing nature to run its course, but these killings weren't natural.
The only recorded instances of elephants killing rhinos occurred at waterholes, when mothers with young calves felt threatened. But these killings did not occur near waterholes, and inquiries quickly eliminated the park's only two mother elephants from the list of suspects.
"We had to do something. If you balance the two species, rhinos are more endangered," Stuart-Hill said.
The victims were all white rhinos, not the more endangered black rhino. Even so, there are 600,000 elephants in Africa, compared to 4,000 white rhinos. But which of the 75 elephants in the Pilanesberg game reserve were guilty?
The breakthrough came when scouts in a helicopter sighted an attack in progress and swooped in. Their priority was to rescue the rhino, which was winched up to safety, treated at a hospital and released.
The elephants got away. But an intensive survey over the following days found three teenage male elephants loitering in the area. A decision was made to shoot them.
"It was difficult," Stuart-Hill said. "We couldn't say definitively that these were the guilty elephants. All we could say is that they were in the vicinity when an attack took place."
The rhino killings stopped, and the case appears closed. But scientists are left to figure out the most baffling question of all: What motivated these elephants to behave in such a savage and uncharacteristic fashion?
The answers they are coming up with would not surprise criminology students in the United States. They also offer no real assurances that the rhinos are out of danger.
In the late 1970s Pilanesberg became a pioneer in the restocking of animals. Baby elephants that would have been marked for slaughter in other parks (as part of the annual cull to keep elephant populations manageable) were moved instead to Pilanesberg along with two adult females to care for them.
Mothers normally drive male elephants from the herd once they reach adulthood. Males start drifting away around age 15, eventually linking up with other groups of male elephants led by a patriarch.
But now that Pilanesberg's elephants are reaching adolescence, there are no adult males for them to follow. Thus, they have become juvenile delinquents deprived of adult supervision or role models.
"There are no adult bulls around to keep them in check," Stuart-Hill said. "So they're highly aggressive and are testing their strength on other animals."
Clive Walker, chairman of the Rhino and Elephant Foundation of Africa, believes the problem goes back to the childhood trauma suffered by these translocated elephants and to the lack of parental authority throughout their formative years.
As babies, these elephants watched their parents being slaughtered, he said. Then they were trucked away from their homes and released into unfamiliar surroundings.
"These are highly intelligent animals with a high level of memory retention and strong emotional attachments," Walker said. "The culling experience is highly traumatic."
Moreover, the two matriarchs in Pilanesberg cannot provide adequate care for the 70 or so junior elephants there.
Stuart-Hill rejects such a sociological interpretation. He prefers a biological explanation: the sudden surge of hormones in adolescent elephants that produces aggressive behavior normally controlled by older males.
If he is right, the killings might have stopped only because the mating season ended. He conceded that three innocent elephants might have been killed and that the problem could resurface next year when the mating season resumes.
The white rhino, hunted to the brink of extinction earlier this century by humans, then would be facing a new threat to its existence from bands of unruly, juvenile-delinquent elephants.
But Stuart-Hill stressed that so far, this is pure conjecture. "We really don't know. It's all still very mysterious," he said.