By Phil Mercer BBC reporter in Sydney

Peter Falconio's disappearance remains Australia's greatest unsolved mystery.

It is 12 months since the British backpacker vanished during a roadside ambush in central Australia.

Detectives believe he was shot dead after stopping with his partner to help a stranded motorist on a remote desert highway in the Northern Territory.

The 28-year-old's body has never been found.

It is going to be a very, very hard case to crack given the mistakes that plagued the early part of the investigation

Professor Paul Wilson

One of the biggest manhunts ever undertaken in Australia has failed to solve the puzzle, despite detailed descriptions of the suspect provided by the missing man's girlfriend.

Joanne Lees survived after telling detectives how she escaped from the gunman and hid in the desert for six hours.

Some criminologists fear the truth about what happened to Peter Falconio will never be known.

"It is going to be a very, very hard case to crack given the mistakes that plagued the early part of the investigation," Professor Paul Wilson, from Bond University in Queensland, told BBC News Online.

Joanne Lees was tied up and thrown into a van

He believes the police "were very slow off the mark" by failing to release e-fit and video images of the suspected gunman, with his distinctive drooping gunfighter moustache.

Crime scene experts, says Professor Wilson, should have been drafted in to work alongside specialists from overseas.

A six-week internal review of the case has cleared the police of any major mistakes.

The Northern Territory has the highest murder rate in Australia.

Most are domestic crimes carried out within aboriginal communities and are usually easy to solve.

It seems certain this was someone looking to sexually assault Joanne Lees

Dr Yvonne Skinner

Criminologists believe the Outback force was too inexperienced to deal with a major investigation such as the predatory murder of a young British traveller.

Forensic psychiatrist Dr Yvonne Skinner believes it was a "rare and opportunistic crime" carried out by an extremely violent sex attacker.

"For this man the excitement of the murder and attempted abduction of a female is something so outrageous and daring that would only be matched by the thrill of escape," Dr Skinner, a former prison psychiatrist, told BBC News from her offices in Sydney.

In the past, she added, couples had been targeted by sex offenders who had murdered the male before raping and killing the female.

"It seems certain this was someone looking to sexually assault Joanne Lees.

"She is very lucky to be alive.

An e-fit of the suspect

"She survived because she was very resourceful," Dr Skinner added.

But has the trail that cooled so quickly last July now frozen over?

Dr Skinner believes that in the future the suspect may slip up if he offends again.

And that science may sooner or later provide a breakthrough.

"Forensic techniques are improving all the time.

"It is amazing how quickly they are advancing."

The police remain optimistic too, despite a barren year of investigation and one marked by constant criticism, including withering censure from Miss Lees.

She accused detectives earlier this year of "sitting back" waiting for the public to call in with information on the lone gunman.

It is something that has left a deep scar on all of us

Bardia Badaghi

The Northern Territory's Assistant Commissioner, John Daulby, said at the weekend he was confident the offender would be caught.

A crime that brought panic to young backpackers a year ago now barely registers on the radars of the new generation of travellers.

Bardia Badaghi from the Northern Territory's Youth Hostel Association told BBC News Online from Darwin that while the disappearance of Peter Falconio caused disquiet a year ago, it was rarely ever mentioned.

"Most travellers have forgotten all about it.

"But the people of the Northern Territory never will.

"It is something that has left a deep scar on all of us."