Now-familiar missing-person posters of 13-year-old Daniel's smiling face are dotted around Maroochydore courthouse, imploring people to come forward with information about his disappearance.

The signs are an unmistakable reminder that, despite an exhaustive and resource-hungry police investigation, the high-profile Sunshine Coast case remains unsolved.

It is nearly seven years since Daniel vanished while waiting for a bus along Nambour Connection Road in Woombye, under the Kiel Mountain Road overpass, on the afternoon of December 7, 2003.

This week a coronial inquest, held at the request of Daniel's parents Bruce and Denise Morcombe, has heard about the scale of what's been described as the biggest missing-person investigation in Queensland police history.

'Unprecedented'

Detective Sergeant Tracey Barnes, who provided a 71-page report to the coroner, was yesterday forced to defend aspects of the investigation, including whether officers had acted quickly enough in chasing up new leads.

She told the court more than 100 investigators had worked on the “huge” police operation, interviewing more than 10,000 people.

Detective Sergeant Barnes said she had been an officer for 28 years and had worked on other missing person and murder cases, but the sheer number of police job logs in this investigation was unprecedented.

Job logs are used to record individual pieces of information held by police.

“We would consider 500 job logs in any investigation to be quite a large investigation,” Detective Sergeant Barnes said.

All up, nearly 18,000 police job logs had been generated during the Morcombe investigation, the court heard.

Several people who thought they had seen number plates on strange vehicles in the area were subjected to regression therapy, or hypnotherapy, in a novel bid to extract registration details from their memories.

But these sessions did not turn up anything concrete.

Undercover operation came to nothing

Officers had also obtained a “cell tower dump” showing the details of anyone using their mobile phones to make or receive calls in the area where Daniel went missing.

Detective Sergeant Barnes said this was because police had received information that two people may have been involved, and it was possible the pair had used mobiles to contact each other around the time of the abduction. The details of more than 1500 phone calls were recovered.

“This is probably the largest dump of telecommunications material obtained during any investigation in Queensland,” she said.

But, again, it came to naught.

Police even deployed an undercover operative in a bid to flush out more evidence from persons of interest. The covert investigator moved close to the people being watched and was on duty for about three or four months, but had no success.

Why wasn't DNA tested?

Scientific officers analysed tyre marks and shoe impressions at the scene of the abduction. The shoe marks were identified as belonging to Globe shoes – the type worn by Daniel – and Colorado-brand footwear.

But the tyre imprints were of a “poor quality” and were unable to be linked to any particular brand.

And no DNA evidence was able to be extracted from a cigarette butt found under the overpass where Daniel was last seen.

The court was told members of the public had sent police several items – such as socks, shoes and similar goods – purportedly related to the case, but officers had to set aside material that was unlikely to be connected.

Detective Sergeant Barnes yesterday came under heavy questioning from the Morcombe family lawyer, Peter Boyce, as to why police did not order DNA tests on a bag of clothing handed to the family by a person of interest.

But Detective Sergeant Barnes said the woman who provided the bag was not credible and later admitted to a Crime and Misconduct Commission hearing the clothing was not linked to the case.

“Her credibility was completely destroyed,” she said.

Suspicious characters

Detective Senior Constable Ross Hutton, who spent five years on the case, yesterday gave an insight into seven of the 35 persons of interest in the matter.

A man, codenamed P15, approached police in 2004 to identify two men who had borrowed his silver 1980s-model car around the time of Daniel's disappearance.

He told police the men, labelled P16 and P17, took longer to return the sedan than expected and he was worried they may have used it for other purposes.

All three men were drug addicts and had criminal histories, including one who had previously assaulted a child in a non-sexual attack.

However, Detective Senior Constable Hutton said details of exactly when the car was borrowed and returned were unclear, and “thorough” tests of the vehicle had turned up nothing.

None of the three men could be linked to the crime, he said.

Detective Senior Constable Hutton also explained how police had investigated two men and a woman linked to a borrowed vehicle that had been abandoned at a railway tunnel at Yandina around the day Daniel disappeared.

All three people – P19A, P19B and P19C – were heavy users of amphetamines.

An informant had claimed the car, a squarish Gemini, was originally blue but was later painted white. Witnesses had reported seeing a blue square-shaped car in the area where Daniel was last seen.

However, when police investigators tracked down the car they concluded the colour change was the other way around – the vehicle had been white and was subsequently painted blue.

The inquest continues.