A copybook containing a "Satanic pledge drawing" and a set of rules including: "No talking about Jesus or God, only Satan", was discovered in the home of one of the boys accused of murdering Anastasia Kriegel, the Central Criminal Court has heard.
The Aisling copybook also had a number of pentagrams drawn inside and a list of names including those of the two accused.
The accused, who are both 14, cannot be named because they are minors. They have each pleaded not guilty to murdering the 14-year-old Kildare schoolgirl at Glenwood House, Laraghcon, Clonee Road, Lucan on 14 May last year.
Boy A is further charged with Ana's aggravated sexual assault in a manner that involved serious violence to her. He has pleaded not guilty to that count also.
Detective Garda Donal Daly told Brendan Grehan SC for the prosecution that the copybook was found by gardai who searched Boy B's home on May 24, 2018.
He said Boy B's name was on the front and the subject for the book was, "drawing". On July 7 when Boy B was interviewed by gardai he referred to the notebook, Det Gda Daly said, and gave an explanation of what it contained.
The jury was shown a video of that interview last Thursday and during it, Boy B explained that the copybook referred to a homework club.
He said he called it a "satanist" club because he didn't want certain people to join. The rules, he said, were not meant to be serious.
Showing the copybook to the jury, Det Gda Daly agreed with Mr Grehan that it contained a "drawing of a satanic pledge" with star-shaped symbols in one corner.
On the same page were a number of circles with five-pointed stars or pentagrams inside them, he said. Written on the same page was a description of a volcanic eruption.
He also pointed to a list of names, the first of which was Boy A's and the last of which was Boy B's. Each name had a symbol to the right of it.
Under the title, "rules" was written: "Only pledge hosts can give pledges. Don't talk about it. Act normally like nothing happened. No talking about Jesus or God, only Satan."
Det Gda Daly also told Mr Grehan that he walked from a place where Boy B was first identified on CCTV with Ana to the abandoned house where Ana's body was found.
Under cross-examination, Det Gda Daly denied to Damien Colgan SC for Boy B that gardai were "disingenuous" during their questioning of Boy B.
He accepted that during interviews the air conditioning in the garda station stopped working and the boy's mother complained of the heat.
He said gardai were "very cognisant" of the fact they were dealing with a juvenile but he said the member in charge at the station was responsible for the boy's welfare.
Det Gda Daly further denied that he prevented Boy B from taking a break during one interview after the boy asked his mother to leave and was told his mother had to remain.
Mr Colgan said the boy was uncomfortable and his mother wanted to take a break and Boy B wanted to speak to his solicitor but was prevented from doing so.
Det Gda Daly said he was not prevented from consulting his solicitor and added that were 35 minutes into the interview and were at a "crucial point".
He said he wanted to give Boy B every opportunity to tell the truth and pointed out that they did break about 10 minutes later.
Inspector Damien Gannon told Mr Grehan that he arrested Boy B on July 12, 2018 at 8.15am, five days after his final garda interview.
The trial continues in front of Justice Paul McDermott and a jury of eight men and four women.