The judge in the trial of two teenage boys for the murder of 14-year-old Ana Kriégel has told the jurors they could rely on lies alleged to have been told by the boys as evidence of guilt, only if the prosecution had established there was no other innocent explanation.

Mr Justice Paul McDermott was continuing his summing up of the law and the evidence in the case.

The two boys deny murdering the schoolgirl in an abandoned house in Lucan on 14 May 2018.

The first accused boy also denies violently sexually assaulting her.

Mr Justice McDermott said the prosecution was relying on what it claimed were lies told by the two accused boys as evidence of guilt, particularly in the case of the second boy.

The prosecution case was that the lies were told to cover up guilt and for no other reason.

The judge said the prosecution was entitled to rely on inconsistencies in various accounts given by the two boys, or lies told by them.

He said a series of false denials could be regarded and relied on as evidence of guilt.

But the judge cautioned the jurors against jumping to simple conclusions in relation to the telling of lies.

Lies on their own may not indicate guilt, he said.

In certain circumstances, an inference of guilt should be drawn, but lies had been told in the past by accused people who are innocent.

To rely on a lie, he said the prosecution must establish that the motivation for telling it was the realisation of guilt and fear of the truth and that there was no innocent explanation.

But the judge said people lied for many reasons - out of shame, panic, misjudgement, confusion or to conceal disgraceful behaviour from their family.

The judge said a substantial body of the prosecution case against Boy B was founded on the lies they said he told.

He said in the boy's final interviews, the jurors may find he had made partial admissions.

But he pointed out, the boy also denied knowledge of an intention by Boy A to kill Ana and denied involvement in assisting the murder.

He told the jurors that had to be considered by them.

If the jurors thought the boy's version was true or credible, they must acquit, he said. If they thought it was reasonably possible that it was true, they must also acquit.

But he reminded them, that if they rejected all or part of what he said, that did not mean they could proceed to conclude he was guilty. It was not that simple, he said.

He told them they had to stand back and consider all the evidence in the case and they could only convict if they were satisfied beyond reasonable doubt, based on all the evidence.

He told the jurors to put on "teenage glasses" and consider the garda interviews with the teenagers from the perspective of a 13-year-old boy.

Mr Justice McDermott said the garda interviews were for the jurors to assess and they should not be swayed by the questions asked by gardaí or the submissions made in relation to them by lawyers for either side.

The judge reminded the jurors again that statements made by one person were admissible only against him and not against his co-accused.

Outlining the definition of murder, Mr Justice McDermott said the jurors had to look at all the circumstances of the case.

They had to ask themselves if the prosecution had established an intention to kill on Boy A's part and if they established participation by Boy B and knowledge about what was going to happen.

The judge spoke about the importance of intention.

He said if the jurors had a reasonable doubt about whether there was an intention to kill or cause serious injury to Ana then they had to acquit.

He said intention could arise within a short period and did not require elaborate pre-planning or premeditation.

Mr Justice McDermott said the prosecution was making the case that the murder of Ana was planned in advance.

He told the jurors that the issue of Boy B's presence at the scene had to be considered very carefully.

Presence, he said, was not participation and did not justify a conviction of murder. If you came across a vicious attack and did not intervene, that non-intervention might not appeal to people as very good behaviour, but it was not a crime.

It was different if a person did something preparatory - or assisted for example, in making a victim available for an assault.

That was something quite different, he said, that was an act of participation.

He told the jurors it was crucial to understand the circumstances of the case, and the facts established by the prosecution about what happened to Ana and the participation and knowledge of the accused.

Mr Justice McDermott said this was particularly relevant to Boy B.

He said the prosecution had to establish beyond reasonable doubt that Boy B knew what the other boy was going to do.

If there was any reasonable possibility consistent with the view that he did not have that knowledge, he told the jurors they must acquit.

The judge said they had a large number of pieces of circumstantial evidence before them, including forensic evidence. They had to assess the weight of each of them and assess their combined weight.

In relation to the charge of aggravated sexual assault against Boy A, the judge said this was a sexual assault involving violence or the threat of serious violence or injury or degradation of a grave nature to the victim.

He reminded the jury of the prosecution evidence and told them they must be satisfied beyond reasonable doubt that it was a sexual assault of an aggravated nature in order to convict him.