New evidence has emerged that could clear six young Australians accused of murdering a Peruvian man.

The so-called Peru Six are fighting efforts to make them return to South America to face questions about the death of a doorman who fell from a Lima apartment block in January 2012.

Police and local media allege the Australians threw him out a 15th-storey window after a dispute over a noise complaint.

The ABC's 7.30 has gone to the scene of the doorman's death with an investigator working for the Australians. He has explained why he believes the prosecution case does not work and details evidence missed by police that points to another version of events.

The Australians - Jessica Vo, brothers Hugh and Tom Hanlon, along with Harrison Geier, Andrew Pilat and Sam Smith - are accused of killing Lino Rodriguez Vilchez.

The death was originally ruled a suicide, but investigators reopened their inquiries after a public campaign by Mr Rodriguez Vilchez's brother, Wimber.

He claimed the Australians dragged his brother into their room, bashed him, and threw him to his death from apartment 1501.

The Australians say that is impossible and they have hired forensic anthropologist Jose Pablo Baraybar to fight the case against them.

Mr Baraybar, who worked for the United Nations for 12 years as its resident forensic expert for the war crimes tribunals for Rwanda and the former Yugoslavia, says the layout of the apartment shows the police theory is highly improbable.

"Fine, in the heat of the moment you do something foolish and stupid - in that case you would not take somebody upstairs through a very narrow stairs where two people cannot take one person," he said.

"One person cannot drag an 85-kilogram guy alone, unless you are twice that size, or Superman.

"Then, from all the possible places to take him, to drag him to a narrow cupboard where two people cannot enter side by side.

"If I would be them, to use this stupid example, I would have used the balcony."

Expert offers another explanation for death

The prosecution relies on three pieces of evidence linking the Australians to the doorman: a footprint on the window sill of the apartment, some marks on the atrium wall, and an Australian $10 note found in Mr Rodriguez Vilchez's pocket.

Forensic expert Jose Pablo Baraybar says the police case does not add up. ( ABC 7.30 )

But the prosecution says the $10 note was destroyed in a policeman's washing machine.

Mr Baraybar suggests the other evidence falls apart almost as easily, saying a shoeprint does not fit the theory of an unwilling or unconscious victim.

"The footprint on the widow sill is somebody standing on the window sill, facing the void, for example. What for? To clean the window," he said.

"The police investigation has been inconsistent since the beginning. It has been incoherent. It is an investigation where you're trying to join the dots of things that cannot be joined."

He says there is another explanation that is more logical: Mr Rodriguez Vilchez fell from a service window on the other side of the building.

"On the inspection with the judge we saw something that looks like a handprint... The interesting thing is the following: right below here there are some skidding marks, some friction marks," he said.

Victim's ghost visited brother in a dream

Mr Baraybar has presented his report to the judge investigating the case, but it is unlikely to convince the family of Mr Rodriguez Vilchez.

"I am convinced my brother was murdered," Wimber Rodriguez Vilchez said.

"The only thing I want is for the population of Australia to know the truth. My brother was murdered. That is clear."

Wimber Rodriguez Vilchez says his dead brother visited him in a dream. ( ABC 7.30 )

Wimber Rodriguez Vilchez became convinced of the Australians' involvement after a dream in which his brother visited him.

"I went running to him, to embrace him, 'Lino my brother', and he said, 'Let me go, let me go, don't hold me, they killed me. I didn't want to die'."

He says his brother's ghost also visited their sister.

"Lino said he had been arguing with somebody. His hands were (moving out) and there was a tall man and a short man and a girl.

"After she said, 'my little brother, tell me, tell where did this happen?', and my brother said, 'nine plus six add it up, nine plus six'.

"And so we said, 'hey, it's in the 15th, in the 15th floor, they have killed Lino, let's go to the police and see how the investigation is going'."

People blamed 'put on silver plate'

Mr Baraybar says the flawed Peruvian investigation is unfair both to the Australians and to the victim's traumatised family.

"The prosecution takes the view of the police and builds a case based on nothing," he said.

"The family is not to be blamed because they want answers. They are grieving people, they need closure, and they do not know who to blame.

"In this case, the people to be blamed have been put on a silver plate."

The Peru Six maintain they are innocent and have been ordered to front court in Lima next month after a judge rejected their request to deliver evidence via video-link from Australia.

One of them, Sam Smith, says the group has a feeling that people in Peru hate them over the incident which has also left them traumatised.

"We were just travelling, like everyone does, thousands of Australians do every year, just at the wrong place at the wrong time. It upset us at the time and we've had to relive it now for 18 months," he said.

"You want to go over there... and say, 'look at the evidence guys, we're really sorry for your loss, but we had nothing to do with it'.

"We really just want to move on with our lives."