More than 90 percent of ivory tusks seized by officials come from recently killed elephants, a comprehensive forensics analysis revealed.

This suggests that the ivory trader's common alibi that supplies date from before the trade was banned is likely incorrect, the study said. What's more, the recent surge in elephant deaths in Africa may likely be connected.

"That puts to rest a speculation which has been at the back of everyone's mind," said conservation ecologist George Wittemyer of Colorado State University.

Some experts wonder whether the ivory trade is being fueled by corrupt governments that sell off old ivory from stockpiles or bit by bit.

However, the new report affirms that scientists and governments must concentrate on protecting elephants from illegal poaching.

Carbon Dating

The team of researchers led by Thure Cerling from University of Utah examined at least 231 ivory tusks that were confiscated by officials between 2002 and 2014.

Cerling and his team analyzed the decay of carbon-14 isotope in these tusks to find out when the elephants had died.

Scientists found that only four ivory tusks were more than five years old at the time they were taken. They also discovered that some of the seized tusks were small, indicating that poachers killed young elephants to attract the more valuable older animals.

Illegal Ivory Trade

Cerling and colleagues also determined where and how the ivory tusks were shipped from place to place. They found that in East Africa, the ivory tusks were taken from elephants that died less than a year ago, while in Central Africa, ivory was derived from elephants more than two years old.

This suggests that the road network in East Africa is much quicker than that in West or Central Africa, says Tom Milliken of wildlife monitoring group TRAFFIC. It allows poachers to get the ivory tusks to the coast faster and ship them to Asia.

Illegal Poaching

The illegal ivory trade is taking a toll on Africa's elephant population, with statistics showing that numbers fell from 496,000 to 352,000 between 2007 and 2014.

Tanzania lost 60 percent of its elephants in the last three years due to illegal poaching, the International Union for Conservation of Nature reported.

"The extinction of elephants and other wildlife due to demand for illegal wildlife products is a major problem," said Cerling.

Cerling said if all the ivory seizures are recent, he and his colleagues can use it to calculate the overall killing rate of elephants in Africa. The data can be helpful in catching illegal poachers, he added.

The findings of the study will be published in the Proceedings of the National Academy of Sciences.