A 19-year-old Dublin man, who wrote letters boasting about the shooting of teenage girl Melanie McCarthy-McNamara, has been found guilty of her murder and jailed for life.

Daniel McDonnell had admitted writing two letters and graffiti while in custody in which he boasted about the killing.

However, he denied a charge of murder.

His lawyers said there was no evidence against him apart from the letters, which were described as "rants".

Melanie, 16, was shot in the head as she sat in a car with her boyfriend and a friend at Brookview Way in Tallaght on 8 February 2012.

After his arrest, McDonnell wrote of the victim's boyfriend: "I will do 25 while you're crying ... two in the head ... your b***h is dead ... little did he know I had a loaded 12 gauge ... left his b****h all over the Sunday World front page.

"I will never forget that mug crying, best night of my life."

He also wrote in a letter to his girlfriend: "I feel like a scumbag ... I am one ... that other thing wouldn't have happened if I'd known she was in the car. It was meant for that other smell bag. He won't get away with bullying my Ma."

After just over four hours of deliberation, a jury at the Central Criminal Court found him guilty of murder by unanimous verdict.

The victim's godmother Jennifer Roche gave a victim impact statement on behalf of Melanie's parents and siblings.

She described her as "the sweetest, prettiest girl you could ever see" and a dream daughter.

"She was everything to us and we will never know why she was killed. She touched the hearts of the world. We love and miss you so much we will never forget you," she said, adding that her parent's world fell apart when Melanie was murdered.

The court was told McDonnell had a number of previous convictions for offences including firearms possession, theft and threatening and abusive behaviour.

In closing arguments yesterday, defence counsel Patrick Marrinan said there was not a scintilla of evidence against the defendant apart from the letters.

The prosecution had not ascribed a role in the murder to his client yet the letters they relied on seemed to place the gun in his hands.

He said a witness who knew McDonnell said he had never seen the gunman before.

The alleged confessions were uncorroborated and later denied by the defendant, he said.

They were made in the context that he was being told he would go down in history and be known as the gunman, Mr Marrinan said.

Prosecuting counsel Brendan Grehan said no finger prints were found on the gun or the car. He described the letters as "truly extraordinary".

He said there was no other explanation other than admissions of guilt and the jury was entitled to convict him of murder.

Mr Justice Paul Carney told the jury there was a total absence of corroboration in the case.

However, they were still entitled to convict on the documents being offered as a confession if they believed they were reliable.