Boy B's defence team claim that he was subjected to "manipulation and pressure" by Gardai when he gave statements that were used to convict him.
He was 13 when he lured Kildare schoolgirl Ana Kriegel to her death in Lucan in May 2018 and was convicted the following year.
The legal team for Boy B today asked for permission to introduce fresh evidence for an appeal against his guilty verdict.
They say that the prosecution team relied heavily on those garda interviews and without them, there would have been "almost no evidence against him"
They also claim that it was assumed that Boy B was intelligent and articulate, but they say this is not the case.
Meanwhile, the prosecution says no new evidence should be allowed in the appeal.
They say Boy B continuously changed his statements when he was presented with new evidence and that Gardai always took into account that they were dealing with a minor.
A judgement will be made before the end of the month.