A boy found guilty of murdering Ana Kriegel now accepts he caused her death but still denies sexually assaulting her, a court heard.
The now 15-year-old, known as Boy A, also expressed he was sorry for what happened and wished it never occurred.
The Central Criminal Court heard from Boy A's paternal grandfather who said he had sincere sympathy for the Kriegel family. "I can't imagine how devastating their loss must be for them," he said.
Boy A's grandfather said that having listened to Geraldine Kriegel speak "so eloquently and passionately", nothing he could say would come close to addressing what she had said.
"On behalf of our family, I would like to express our sincerest regret and remorse," he said.
"I know [Boy A] is incredibly, very sorry for what happened and wishes it never occurred."
The man said he was "personally heartbroken" his "much loved grandson" would be involved in such an act.
He said Boy A had never before been in trouble and had never shown any aggression or anger.
"There will be a major gap in all our lives without his continued presence," he said.
The grandfather also said the lives of Boy A's family had been "turned upside down" and they were "enduring great emotional turmoil and loss".
The teenagers, known as Boy A and Boy B, were found guilty of murdering Ana Kriegel at an abandoned farmhouse in Lucan on May 14, 2018.
Earlier, prosecution counsel Brendan Grehan SC led Detective Inspector Mark O'Neill through the evidence.
In garda interviews, Boy A made no admissions and denied ever being in the farmhouse, the court heard.
However, in reports from healthcare professionals prepared after his conviction, Boy A now appeared to have accepted he caused Ana's death.
Insp O'Neill agreed with Mr Grehan that Boy A described a headlock, chokehold, kicks and of hitting Ana with a stick.
Boy A also described hitting her with a block, either throwing it at her head or hitting it off her head three times.
However, Boy A continued to maintain he did not sexually assault Ana, and offered alternative explanations for some of her injuries.
Insp O'Neill agreed with Mr Grehan that there was still no consensus, in particular to the planning and pre-mediation that gardaí found in the course of their investigation.
He agreed that there were disputes between the boys' accounts in relation to whose idea it was to meet Ana, who decided Boy B was to call for her, and who decided where they were to meet up.
The defendants were also in dispute about how Ana's clothing was removed, who smashed up her mobile phone, who produced the tape and put it on her neck, and how they came up with similar accounts as part of the "cover-up" afterwards.
Mr Grehan put it to Insp O'Neill that there was no clear explanation as to why this had happened, and the garda replied: "No, there isn't."
Boy A's counsel, Patrick Gageby SC, said he was conscious that no sentence passed by the court could in any way afford relief for the Kriegel family.
Counsel said it was for the court to select a punishment and it was not for him to suggest what it could be, but he said the court would have to chart a course that was punitive but also gave the possibility of rehabilitation.
Mr Gageby said his client was studying for his Junior Certificate, and would possibly sit it next year.
He said Boy A came from "a good family", "a small, close, loving family".
Reports conducted during his detention at Oberstown suggested there was no emotional causation for the crime and nothing was found to suggest any class of a psychiatric order.
He said there had been "substantial remorse and tears" when the subject was discussed during his detention.
Mr Gageby said all the reports commissioned gave the opinion "there is much work to be done here" with Boy A.
"A high level of intervention is warranted, perhaps to be spread over years," he added.