An American woman who survived a massacre in Uganda is "relieved", yet "sad" two men once accused of carrying out the atrocity have been resettled in Australia.

Elizabeth Garland was conducting research in the Bwindi Impenetrable National Park in March 1999 when eight Western tourists were brutally murdered by Rwandan rebels.

She survived by hiding for several hours as between 100 and 150 fighters armed with machetes, axes and guns rounded up visitors and marched them into the jungle.

"I could have very easily been captured and killed myself," Dr Garland said, adding that American and British nationals were targeted.

"I have thought many times about what it would have been like."

During an FBI terrorism investigation, three Rwandan men eventually admitted to being involved in hacking two American tourists to death.

A burnt-out 4WD stands abandoned at the entrance to mountain camp of Uganda's Bwindi National Park in 1999. ( Reuters/Stringer )

They were extradited to the United States, where prosecutors pushed for the death penalty.

But Dr Garland said she always had doubts about the case.

"It seemed very improbable that they would have caught the men that did the killing of the American victims, given the number of people involved in the attack," she said.

"It always seemed like quite amazing odds. I was worried these men were just being used as pawns in the US war on terror."

The case collapsed in 2006 when a judge ruled the confessions had been obtained via torture in Rwandan prisons.

The men refused to return home for fear of persecution and the US Government would not grant them asylum.

They remained in limbo in immigration detention until the end of last year, when two were resettled in Australia as part of a refugee swap deal first negotiated by the Obama administration and former prime minister Malcolm Turnbull.

One man remained in detention in Florida.

"I have no idea if these men were guilty but I do know the case was so weak against them that the charges against them were dropped," Dr Garland said.

"I also know they have been tortured ... and imprisoned now for a very long time. So, I was very relieved to have them released."

A leaked transcript of a heated first phone call between US President Donald Trump and Mr Turnbull revealed the former Australian leader had pledged to "take anyone that you want us to take" as part of the agreement.

"The only people that we do not take are people who come by boat," Mr Turnbull reportedly said.

Families of victims devastated by deal

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 2 minutes 11 seconds 2 m 11 s David Roberts's son Steven was killed in Uganda by Rwandan terrorists in 1999

Relatives of the victims in Australia and the United States were outraged when it emerged the Rwandans had been resettled last week.

Perth man David Roberts, whose son Steven was among those murdered, said the Federal Government had let his family down.

"[These men] shouldn't be walking around anywhere in Australia or anywhere else," he said.

While DeAnne Haubner Norton, the little sister of slain American man Rob Haubner, said she was shocked Australia would want to exchange refugees for the Rwandans.

"I don't think it's right. These men should have been sent home to face whatever consequences awaited them," she said.

Americans Rob Haubner and Susan Miller were both killed by Rwandan militants. Archive photo ( AP )

The Government has repeatedly defended its decision to accept the pair.

Prime Minister Scott Morrison said they had undergone checks relating to national security, criminality, war crimes and crimes against humanity.

"That resulted in an assessment that they did not represent a risk," he added.

Dr Garland sympathised with the families of the victims and said it was a pity Australia was the country the Rwandans were sent to.

"The fact it was Australia seemed very sad and unfortunate to me because ... these men are now closer to some of the victims' families," she said.

"This just seemed like a very difficult thing for families... to have this grief resuscitated and to have it caught up in Australia's already divisive immigration debate."

The massacre occurred just five years after the Rwandan genocide had ended and the Ugandan forest was becoming increasingly popular with international tourists who wanted to see mountain gorillas.

War was also just beginning to break out in eastern Congo.

At the time, Dr Garland was researching what the local people thought of the tourist trade, given the violence and death nearby.

She remains in contact with some of them.

"I was terrified. I thought [the rebels] would find and capture me," she said, reflecting on the attack.

"So, it's not an easy thing for me to dismiss, the anger and grief the family members are feeling."

However, Dr Garland said her feelings on the attack had been changed by her work on international human rights issues.

"I just think that in these very divisive times we are living in that the rule of law, due process, provide us with protections from the abuse of power by states," she said.

"So, I think it is a good thing to have [the men] out of indefinite detention."