The jury in the trial of a man accused of murdering teenager Mariora Rostas has begun hearing closing arguments from the prosecution and the defence.

Prosecuting counsel Sean Gillane has told the jury that the case involved a "journey through the heart of darkness".

Ms Rostas went missing on 6 January 2008 while begging in Dublin city centre.

She had been in Ireland for 18 days.

The 18-year-old died from gunshot wounds to her head.

Her body was buried in a shallow grave in the Dublin/Wicklow Mountains, where it was discovered four years later.

Alan Wilson of New Street Gardens in the city has pleaded not guilty to murdering Ms Rostas at Brabazon Street, The Coombe between 7 and 8 January 2008. 

His friend Fergus O’Hanlon has told the trial he helped him to bury the body.

In his closing argument Mr Gillane said it was difficult for ordinary people to see things through the lens of the chief prosecution witness Fergus O’Hanlon, who was involved in burying the body of the teenager.

There was a temptation to be sniffy and ask what the prosecution was doing relying on his evidence, but he said the context was important.

He said in that context the evidence the prosecution relies on was "never going to be from an altar boy or a choir boy". 

He said the jury would have to assess his motivation for giving the evidence.

Mr Gillane said Mr O’Hanlon did not have to look for immunity in return for information about the accused man Alan Wilson because he already had the "gold standard immunity".

He said if you worked on the premise that Mr O’Hanlon had killed her then he had gotten away with it in 2008 and did not need immunity.

Mr Gillane said Mr O'Hanlon in 2011, despite being told by his solicitor that he could be prosecuted, still wanted to assist gardaí to find the girl's body.

He said Mr O’Hanlon's solicitor had made it clear there were no deals on offer for immunity.

He said in law Mr O’Hanlon was an accomplice and the jury would be warned about the dangers of convicting on the uncorroborated evidence of an accomplice.

However, he said there was corroboration to be found in the evidence about the ownership of the car which was registered to the accused man, Mr Wilson.

He said the murder was an execution. "It was cold, calculated and precise with every scrap of evidence meticulously, comprehensively and successfully destroyed."

He said it was not a crime of passion, of temper or of loss of control, it was the exact opposite.

"The DPP invites you in the light of the evidence to find Alan Wilson guilty of the crime of murder".

He said "guesswork and speculation" leads to the wrong results. 

Defence Counsel Michael O’Higgins said it was a "one witness case" and to bring in a conviction they had to be satisfied that witness was telling the truth.

He told the jury to "forget about altar boys and choir boys" and that he would take the commonest street thug if he gets into the witness box and tells the truth.

He said Mr O’Hanlon had lied about the first and last issues put to him in the witness box and this had "bookended" his evidence, which was full of lies and contrived lies.

He told the jury to consider the photo fit image generated from a description given by Ms Rostas' brother, which he said bore a very strong likeness to Mr O’Hanlon.

He said it was significant Mr O’Hanlon had refused to take part in an identification parade.

He also said Mr O’Hanlon had use of Mr Wilson's car.

There was evidence that Mr Wilson often gave him phones, motorbikes and had eventually given him the car in question which was of potentially great significance, he said.

He asked if Mr Wilson had bought all the materials to clean up the scene as alleged, "why on earth would he keep the car" used to dispose of the body”?

He said evidence from a phone call Ms Rostas made the day after she disappeared during which she called out letters from a street sign could have been Brabazon Street where Mr O’Hanlon lived.

This could connect her while still alive to Mr O’Hanlon just as the photofit connected him, Mr O’Higgins said. 

The defence will continue its closing argument tomorrow.