The clues that snared a murderer

But detective chief superintendent Craig Dobbie said the teenager was nothing more than a witness at the beginning of the investigation.

It wasn’t until inconsistencies emerged in his statements that he became a suspect.

He said they tried to eliminate him from their enquiries but "they just couldn’t".

Mr Dobbie, 53, said more than 3000 statements were taken throughout the course of the inquiry.

"We interviewed everyone possible," he said. "We interviewed every male who had been viewed with general suspicion.

"That group included any males known to Jodi - both relatives and friends.

"Luke was one, and, at first, he was no different from the rest of them. We were just trying to eliminate people from that group.

"It wasn’t until July 3 that our suspicions about Luke increased. We had a degree of suspicion, but not enough to detain him.

"Things were starting to piece together - things his school friends were saying about him carrying knives; the sighting by the witness Andrina Bryson - who claimed she had seen Luke with a girl standing at the top of the Roan’s Dyke path on the day she was killed; and, most importantly, the difference in the statements given by Jodi’s family about how Jodi’s body had been found and Luke’s version of events.

"However, we still had to be aware that Luke was providing a statement voluntarily and that he may have been deeply traumatised at the time."

The next day, Mr Dobbie asked for Mitchell to be interviewed again - this time under police caution.

"We made it clear he was under caution - it was only fair to him to do so. This was when he further entrenched his position.

"This was a few days on after the killing so what he was saying at this stage was probably more accurate.

"There were critical differences in what he was saying about when the body was found. The family were consistent in their evidence.

"They all said Luke never walked past the V in the wall before climbing over and discovering the body. But Luke’s version was completely different.

"He said he walked past the wall a considerable distance and the dog reacted at the point relating to where Jodi’s body was.

"We couldn’t get away from this conflict in versions. We tried to eliminate Luke from our inquiries but we just couldn’t."

The next piece of information which gave detectives cause for suspicion concerned the wood burning stove in the Mitchell’s back garden.

Mitchell told police that his mother Corinne and brother Shane were using the stove that night. Corinne said it was not being used and Shane was not able to say either way. "We also had reports from neighbours saying they had smelled burning coming from the Mitchell’s back garden that night," said Mr Dobbie.

"Then there was the parka jacket," he added. "We spoke to friends, school teachers and others who knew Mitchell and established he had a parka jacket. The eye witnesses had also made references to a long parka style jacket. His mother said he had never owned one.

"When we searched the house, the parka was missing.

"But friends and family were adamant that he owned one. We also had the information about the wood burner and we started to paint a picture."

However, Mr Dobbie did not want to detain Mitchell until the DNA test results had come back from the lab.

"When the results came back there was not one DNA profile which could not be accounted for. Every profile belonged to people who knew Jodi, including Luke. However, what we didn’t have was DNA from someone unknown, which ruled out anyone unknown as the killer."

Mr Dobbie said: "In August we detained Luke for further questioning. We searched his house again and his father’s house but still there was no evidence of the jacket that we believed to have existed before the murder, or of any knife.

"At this stage, unless Luke gave us a confession or took us to the knife, we did not want to arrest him. We did not want to go down that road unless we were 100 per cent confident the circumstantial evidence we had was correct.

"It wasn’t until October that we believed that we had grounds to report Luke to the procurator fiscal for a circumstantial case.

"After carrying out their own investigations, and interviewing witnesses they supported us and, eventually, a warrant was issued for Luke’s arrest in April, 2004."

It was on this day that Mitchell’s house was searched again and Shane Mitchell admitted he had been looking at porn on the internet on the day of Jodi’s death.

He said he would not have done this if there was other people in the house - which did not support Luke’s alibi that he was at home with Shane at the time Jodi was killed.

Mr Dobbie said: "When we searched the house we also found a knife pouch with the inscription ‘JJ 1989-2003’ and the numbers 666 written on it and one of Jodi’s favourite quotes. It was like some kind of memorial to Jodi.

"We made inquiries and discovered that Mrs Mitchell had bought a knife which came with a pouch identical to this one in December 2003. She said she had bought it for him to go on a camping trip. But why purchase that knife. It seemed bizarre, bearing in mind Jodi had been killed and that her son was a suspect.

"We started to question whether that knife was a replacement to one he had previously."

But today as Mitchell was found guilty, Lothian and Borders Police’s hunch was proved right, although there was severe criticism of their handling of the investigation during the case.

There was no murder weapon, no blood covered clothes - despite the gruesome nature of the murder - and no damning DNA find.

There was not even convincing eye-witness testimony.

The trial heard that Jodi’s body was left uncovered and exposed to the elements for eight hours after it was first discovered, possibly risking the destruction of vital DNA evidence.

The schoolgirl’s body and items around it had been moved before the forensic team started work.

Even though the knife used to murder Jodi had not been found, the bins in the area were allowed to be emptied before a thorough search could be carried out.

The way police carried out a virtual identity parade, presenting photographs of Luke and other youths to one witness, was also criticised during the trial at the High Court in Edinburgh.

A string of incidents were highlighted by Mitchell’s defence lawyer Donald Findlay, QC, during the 42-day trial.

In one blistering courtroom attack, Mr Findlay described the behaviour of detectives as "a disgrace".

The court heard that the first forensic scientist to examine the crime scene arrived more than eight hours after Jodi's body was found. Not only had her body been left uncovered overnight in the rain, but it had also been moved and items around it moved before Derek Scrimger arrived at the scene.

Under questioning from Mr Findlay, Mr Scrimger was forced to admit that it was "not an ideally managed crime scene from the very start".

The forensic scientist said he believed that a tent should have been erected over the scene.

Mr Scrimger’s work was further delayed because an earlier female colleague had arrived at the scene, but could not get over the wall to get to the body because she had a bad back.

The jury also heard that a pioneering lab using the most sensitive DNA test in Britain failed to identify Mitchell as the

It also emerged that detectives probing the murder broke normal guidelines by not putting Mitchell on an ID parade.

Mr Findlay claimed "a tactical decision" had been taken not to treat the boy fairly.

But today detective chief superintendent Craig Dobbie launched a vigorous defence of their detective work.

Mr Dobbie described the crime scene as one of the "finest I have ever seen".

He said that every care was taken to recover every single piece of evidence that was there.

And he defended claims made in court that the scene was not well managed.

Mr Dobbie admitted that the case against Luke Mitchell was purely circumstantial, but insisted Lothian and Borders Police Force had done a great job.

"We have been scrutinised by one of the finest defence lawyers in the country, but not one point has been inadmissible.

"I am open to suggestions as to where we could have made improvements in the investigation, but I can’t think of anything obvious."