A boy told Garda interviewers that his co-accused told him he was planning to kill schoolgirl Ana Kriegel but he didn't think he was being serious, a trial heard.
Boy B said Boy A had approached him the month previously and said to him "hey, wanna kill somebody?".
Boy B told gardaí he said "no", and told Boy A it was "retarded". Boy B also said his friend was wearing a "zombie mask" when he assaulted Ana.
Asked why he didn't say anything to gardaí when they called to his house investigating Ana's disappearance, Boy B said he was "scared".
He also said he was afraid of "being framed by [Boy A]" and he was "ashamed" as he had run away and not helped Ana.
The accused, who were 13 at the time, have pleaded not guilty before the Central Criminal Court to murdering Ana Kriegel at Glenwood House, Laraghcon, Clonee Road in Lucan on May 14, 2018.
Boy A has also denied a charge of aggravated sexual assault.
Yesterday, the jury finished watching video footage of interviews which gardaí conducted with Boy B after he was arrested for a second time on suspicion of the murder of Ana.
The interviews took place at Lucan garda station on July 7, 2018. Present during the interviews were Boy B, his mother, his solicitor Barry Powderly and Detective Garda Donal Daly and Detective Sergeant (now Inspector) Damien Gannon.
Boy B told gardaí other friends told him that Boy A had said he was going to kill someone, but he didn't think he was serious.
Boy B said Boy A had also approached him the previous month and said to him "hey, wanna kill somebody?".
Boy B said he told him "no", and it was "retarded".
Boy B said he had asked Boy A who he was planning to kill and he [Boy A] told him Ana Kriegel.
Boy B said he replied: "In your dreams". Boy B told gardaí he thought Boy A was messing, and he knew he wasn't being serious.
This was because he and his friends "joke around all the time" and never mean stuff, he said.
Boy B said that when Boy A asked him to call for Ana on May 14 he [Boy A] told him it was relationship issues.
Gda Daly put it to Boy B that he had to tell the truth.
"I didn't know what Boy A was planning," Boy B said.
Asked why he did not go for help when he realised what was happening, Boy B said he was "scared" and "shocked".
"My brain was frozen, frozen in place. I didn't know what to do," he said.
Gda Daly put it to Boy B that he could have saved Ana. "I know," he said.
Asked why he did not try to save her, Boy B responded: "I don't know."
Boy B also told Gda Daly he was ashamed for running away and not helping Ana.
Asked why he didn't say what had happened when gardaí called to his home investigating Ana's disappearance, Boy B said he was "scared to tell anyone".
He said he "just tried to forget about it" and tried to pretend that nothing had happened.
"You made up stories," Gda Daly said.
"I was scared," Boy B said.
"Scared of what?" Gda Daly asked.
"I was scared of being framed by [Boy A]," he said.
In the final interview with gardaí, Gda Daly asked Boy B to "tell me the truth".
Boy B said Boy A asked him to call for Ana, citing "relationship issues".
Boy B said he and Ana walked through the park to the Lucan Road, and towards the house.
He said Ana and Boy A stopped near the house and he walked inside to explore, before he came back out.
Boy B said Boy A and Ana then walked inside the house. He was told to leave, but he didn't want to go, though he didn't tell Boy A that.
He said he then heard "shuffling" and he went and stood at the door of the room Boy A and Ana had gone into.
"I stood still. I couldn't move. I couldn't do anything," Boy B said.
Boy B said Boy A started stripping Ana and once he got to her bra he looked up at Boy B and that's when he ran.
Boy B said he didn't know why Boy A had targeted Ana.
Asked why he didn't tell anyone what he'd witnessed, Boy B said he was "too scared to tell anyone".
Asked why he didn't say anything to gardaí, Boy B said he was too scared to admit he didn't help Ana and was too stupid not to realise what was going on.
Boy B also said he didn't recall seeing Ana's blood.
"Ana's injures were not paper cuts," Gda Daly said. "Do you expect us to believe you didn't see any blood?"
Boy B answered: "From my point of view I didn't see any blood."
"I told you the truth. I told you everything I saw, everything I remember," Boy B said.
Gda Daly put to it Boy B that he brought Ana to the abandoned house.
"You brought the prize. You brought her. You lured her to her death, didn't you?" Gda Daly said.
"No," replied Boy B.
Earlier, Gda Daly showed a photograph of a mask to Boy B.
Boy B called it the "zombie mask" because he said that's what Boy A called it.
Asked if Boy A was wearing the mask, Boy B responded: "Yes, he was wearing the mask."
The trial continues this morning.