A trail of DNA has helped investigators trace the biggest ever consignment of contraband ivory seized since 1989 to savannah elephants in Zambia.
Scientists extracted DNA from 37 tusks recovered from the shipment, which was seized in Singapore in June 2002.
They compared this data against a continent-wide map showing genetic differences and similarities between African elephants.
Details appear in Proceedings of the National Academy of Sciences journal.
The 2002 seizure in Singapore consisted of 532 tusks packed in a 20ft container that had been shipped to the Far East from Malawi in south-east Africa.
It also contained 42,000 hankos, small blocks of solid ivory used to make signature stamps, or chops, that are popular in China and Japan.
The Singapore haul was the second largest cache of captured illegal ivory on record, the biggest since the 1989 ban, and represented ivory from 3,000 to 6,500 elephants.
But this represented just a snapshot of a potentially devastating threat to Africa's wild elephant population, said Dr Samuel Wasser, the study's lead author.
"Elephants are majestic animals and are not trivial to the ecosystem," said Dr Wasser, from the Center for Conservation Biology in Seattle, Washington.
"They are a keystone species and taking them out significantly alters the habitat."
Authorities assumed that the ivory had been collected from many different parts of Africa, and especially from forest elephants.
But analysis of DNA taken from the tusks showed this was not the case.
The researchers compared genetic sequences from the tusks with those in a database of DNA sequences from African elephants whose geographic origin was known.
The results showed that the ivory came from savannah elephants in a small region of southern Africa, with Zambia as the focal point.
The tusks weighed an average of 11kg each, more than twice the weight normally seen in the market, indicating that they came from older elephants.
China's rapidly expanding economy is thought to be a major force driving the black market ivory trade. In 1989, a kilogram of high quality ivory sold for US$100 (£51).
The price rose to US$200 (£102) in 2004, but by last year had soared to US$750 (£382).
The African elephant population plummeted by 60%, from 1.3 million to just 500,000 between 1979 and 1987, largely because of ivory poachers.
It is estimated that more than 23,000 elephants were killed to produce the contraband ivory uncovered in 12 separate seizures in the year August 2005-2006.