By Russell Findlay

Cold, cocksure and composed, Alesha MacPhail's teenage killer maintained a mask of innocence from the moment he first became a suspect right up until the inevitable guilty verdict.

As he sat in the dock of the High Court in Glasgow he could have passed for a fresh-faced, preppy university student who had been inconvenienced by a minor scrape with the law.

Wearing a smart suit and tie, poised and respectful, he was a perfect study of neutrality, all with one purpose - to convince the jury that it was all a terrible misunderstanding and that he was innocent.

Watching this chilling act, it was sometimes easy to be taken in, to forget the horrors that this outwardly respectable and supremely confident young man had so obviously committed.

Flanked by two security guards, he was on trial for the most horrific of crimes - the abduction, rape and murder of a six-year-old child who was stolen from her bed, sexually brutalised then killed.

According to leading Scottish criminologist Professor David Wilson it is easy to understand why jurors may have been fooled by a youth who does not match the stereotypical idea of what we expect child rapists and killers should look like.

He said: "There's this failure in the popular imagination to understand that murder is a very complex phenomenon rather than a simple one.

"Murderers come in all shapes and sizes. The idea that a murderer can't be like this or act in a certain way is simply wrong."

Thankfully, the eight women and seven men of the jury - sitting on what prosecutor Iain McSporran called the "worst of cases" - were not fooled by his superficial charm and returned an unanimous guilty verdict.

They had heard extreme, disturbing and damning testimony including injuries to Alesha's genital area described as "catastrophic" and the killer's DNA all over and inside her body.

They had firmly rejected the killer's outlandish bid to blame Toni McLachlan, the 18-year-old partner of Alesha's dad, for the killing.

Giving evidence without a flicker of nerves, the killer had an answer for everything put to him.

He calmly asserted that he had sex with Toni and that she was driven with jealousy of the beloved little girl - had murdered her and planted his DNA in her body.

This was surely among the most outrageous and offensive defence cases ever heard in a Scottish court.

Professor Wilson, of Birmingham City University, also understands why the killer determinedly spun such an incredible lie in a bid to walk free.

He said: "There is some talk about this being about drugs but it is far more to do with rape and sex.

"This is a young man being unable to come to terms with the realisation that he had raped a little girl and only way he could deal with that was to kill her.

"This is is a lot about denial and how it allows the person to continue to lie and their life being able to exclude the truth from entering into their conscious world.

"That is what motivated him to tell this lie and if he is ever allowed safely back into the community then a great deal of work needs to be done for him to accept the truth."

Parallels can be drawn between Alesha's murder on the Isle of Bute last summer with another child killing more than half a century ago - the rape and killing of eight-year-old Catherine Reehill in Glasgow in 1961.

A 16-year-old called Angus Sinclair decided to plead guilty to Catherine's culpable homicide.

We now know that Sinclair went on to become one of Scotland's most prolific serial killers and that when he dies behind bars he will take the true number of his victims to his grave.

But any temptation to compare Alesha's killer to Sinclair should be treated with caution.

While Alesha's killer committed a similarly extreme crime of sexual violence at the same young age and his calculating nature was on display over eight days in court, he may not fit the template of a serial killer waiting to happen.

Asked if Alesha's killer would have gone on to kill again, Professor Wilson said: "No, but I can understand why people would say that."

The fundamental difference between Alesha's killer and the likes of Sinclair was his lack of planning - which left behind what the prosecutor described as a "mountain of evidence".

"All the offenders of this nature who I speak to in prison watch TV programmes about forensic techniques and they all know there are certain things you do and don't do in order to get away with a crime', said Wilson.

"This type of knowledge is pretty standard and I think that he would have been a lot more careful about how he went about this.

"This is much more about the inability to accept what he did. He would have been a lot more cunning and calculating.

"He did not think it through. He would have read all the books and not left such a large amount of incriminating evidence."

While the teenager's name will remain unknown to the general public until legal protection ends when he turns 18, it will be on the lips of every prisoner in Scotland.

And as he is set to begin a life sentence, he will find out that all the self confidence in the world will count for nothing.

In prison, a child killing rapist is just that ... no matter how good a liar he may be.