At least some of the people killed when Malaysia Airlines Flight 17 were AIDS researchers and activists heading to a conference in Australia. That much is confirmed. Beyond that, much is unknown.

News reports have estimated that more than 100 people on the plane — nearly a third of the 298 passengers killed in the crash — were heading to the conference, a number cited by President Obama during remarks on Friday. But conference organizers said that they had only been able to confirm the names of seven people so far, cautioning that the number of people on the plane heading to the conference may be lower than the figures that have been reported. (About 14,000 people are expected at the conference.)

“We have been working hard to try and confirm how many people were on the flight,” Chris Beyrer, who will take over the presidency of the International AIDS Society next week, told The Washington Post. “We’ve been speaking to a number of different authorities, and we think the actual number is much smaller.”

President Obama, speaking at the White House, called the deaths of nearly 300 people an “outrage of unspeakable proportions.” He highlighted the passengers heading to the AIDS conference during his remarks, praising these passengers as people focused on helping others.

“On board Malaysian Airlines Flight MH-17 there were apparently near 100 researchers and advocates traveling to an international conference in Australia dedicated to combating AIDS/HIV,” he said. “These were men and women who had dedicated their own lives to saving the lives of others, and they were taken from us in a senseless act of violence.”

When asked where President Obama got the “near 100 researchers and advocates” figure, the National Security Council told The Washington Post that the figure was used in remarks by Australian Prime Minister Tony Abbott.

But The Post has been unable to locate any remarks where Abbott specifically cited this figure. In addition, Australian Foreign Minister Julie Bishop does not appear to have used the number directly, instead saying only that “a number of people” heading to the conference were on the plane. (We will update this post if we find any remarks where Abbott or Bishop cited the figure.)

Victoria Premier Denis Napthine told reporters in Melbourne that the exact number is unknown, but said “there is no doubt it’s a substantial number.”

The “nearly 100 delegates” figure appears to have originated from delegates at a pre-conference in Sydney. It has not been confirmed or debunked, in large part because the identities of most of the passengers remains unknown.

An official passenger manifest has not been released, slowing the process of identifying who was on the plane. (Malaysia Air said on Friday that it still had not determined the nationalities of four passengers.) So the AIDS conference organizers are relying on information from a variety of sources, including colleagues, friends, family members and government authorities.

Beyrer told The Washington Post that while it is possible some people were on the flight and heading to the conference that organizers did not know about, it does seem the number is “an order of magnitude smaller than what has been reported.”

Caelainn Hogan, Ariana Eunjung Cha and Joel Achenbach contributed to this report.