The youth (15), who cannot be named, has been charged alongside two men, aged 32 and 36, with the killing in west Belfast.

Mr Mongan (30) was hacked and beaten to death in front of his heavily pregnant wife Julia at their Fallswater Street home in February.

As the teenager went before the High Court in a bid to be released, prosecutors claimed he attacked the victim after another of the intruders felled him with a hatchet blow.

"He used a baseball bat to beat Mr Mongan as he was on the ground being hacked," Crown Counsel Amanda Brady claimed.

"The prosecution say the facts of the murder of John Mongan and his alleged involvement in it are so horrific that one could conclude from that its necessary to protect the public from this person."

The court was told the teenager was arrested in Derry the day after the murder, denying any involvement when first questioned by police.

But Mrs Brady said the murder victim's wife had named all three of the accused, claiming to have known them for years.

Defence counsel Martin McCann questioned Mrs Mongan's ability to the recognise the murder gang, telling the court that others reported them to be wearing masks.

Claiming his client had provided an alibi, the barrister also attempted to allay fears he may flee Northern Ireland by emphasising the EU extradition processes now in force.

After hearing both sides, Lord Justice Higgins stated that children charged with criminal offences should normally be released on bail under law, unless in circumstances where the alleged crime is violent or sexual.

He said: "In the circumstances of this case, from what I have been told, this was an offence of extreme violence."

Refusing bail, the judge added: "I have to say, regrettably for a boy of 15 years of age, I consider it necessary to protect the public and, therefore, it's necessary that he be remanded in custody pending his trial for the offence of murder."