David Bain had already planned what he was going to do with the house

On the Thursday, within four days of the murders, David expressed to a friend that he planned to sell the house and buy elsewhere.  This is before the funeral and during a period in which, if he was an innocent bystander, he should be still in grief and such plans unthinkable.  From the 2009 retrial:

Q.    Did you talk about the funerals in any other way as well?
A.    Yep, he knew that he wanted Arawa to wear the ball gown that she was either going to wear or had worn at a ball.  That he hadn't decided about the clothes for the rest of the family yet and that he was hoping to be able to get in the house the next day to be able to go and choose, but he hadn't particularly got any ideas about that.  I’d asked about, you know, what his plans, you know, had he started thinking about what life might be like after funeral and he said that he was thinking he was going to sell the house and buy somewhere for himself so that he would have a home.
Q.    Did he mention where the money was going to come from?
A.    Yeah he was quite concerned that he managed to get the money back from the Meders, because he was a bit anxious that with the amount of money, if it, you know, kept growing with interest and what have you, they would not be in a position to be able to repay it.