The two gardaí who interviewed Boy B went to St Catherine's Park the day before he was arrested for the first time to walk the route they believed he took with Ana Kriégel.
The boy called to her home at 5pm on 14 May 2018.
He said the other accused boy had asked him to bring her to meet him so he could tell her he was not interested in her.
Garda Donal Daly gave evidence that he and Detective Inspector Damien Gannon went to the park on 23 May 2018.
They based the route they took on CCTV footage and on statements from various witnesses.
The two gardaí started near Ana's home and entered the park from the Leixlip side, taking note of the GPS coordinates of various locations along the way.
The route took the two gardaí just under 25 minutes walking at an average pace. Another garda, Marcus Roantree, walked the same route in just over 20 minutes.
Inconsistencies between the first account Boy B gave of his movements, and sightings on CCTV cameras in and around the park, were crucial in getting the boy to admit he had told gardaí a "lie" and a "fake story" about where he originally met Boy A, and how far into the park he and Ana had travelled.
The footage and the timings taken by gardaí along the route proved the boys could not have met up in the park as they had each suggested.
The prosecution suggested the "somewhat similar" stories initially told by each boy about meeting in the park showed Ana's killing must have involved some planning.
Video by Paul Deighan
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