Gerards Forced Error.
From Gerards first call to the police, 7.15am it has always appeared to me to be where the whole 'plan' fell apart.. .it was either too early, if she went for a morning walk or too late if she went for an evening walk. Up until then, he is texting Allison , setting a scene, up now , girls are up, making lunches, where are you, and so on. .some unforseen thing then forces Gerard to start ad libbing, on the fly, and the whole thing starts to unravel. The timing is now all over the place, and out of his control.
In his interview that morning, he says, he knew Allison wanted to be leaving by 7am ,... the seminar began at 8.30am in the city.
at 7.09, he rings Kate Rankin.. he makes a significant slip to Sgt Curtis about this..
BadenClay*....' she was meeting Kate at the office at 8am, which I didnt actually know, but I knew she wanted to leave here at 7am..'
He finds out from Kate Rankin at 7.09, that Allison was going to meet Kate at 8am in the office.. he didnt know this bit of Kate and Allisons plan that morning until 7.09am approx..that is, he didnt know last night or this morning about this detail in the arrangement, but he does now .. assuming 2 mins at the most for this call, he is off and setting a whole other scene.. 4 minutes later, ' I am driving up (indistinct) street , etc.. '
Something about Allison and the arrangement to meet Kate at the office at 8am, which he didnt know before , but now knows at 7.09 am has set a mighty cat among the pigeons, and he has to , or is compelled to, make that 7.15am call to the police.