I think Adam's post #149 must be referring to Chapter 27 page 252:
From the beginning Bamber was trying,according to Miss Mugford,to commit the perfect murder,a murder that would not be discovered. After disregarding a plan to sedate his parents,shoot them and set fire to the house because the insurance cover was too low,he devised a second plan. This was to stage the killings himself,and make it look as if his sister had committed the crime because she was mad. He told Julie he had found a way to get in and out of the house without trace,leaving through a kitchen window which would appear to have been shut from the inside due to the design of the catch. "On the evening before the murders",Arlidge said,"he phoned his girlfriend in Lewisham and said he had been thinking of the murders and decided it would be tonight or never. She told him not to be so stupid."
It's not exactly the same thing as #149 Adam.