Its scripted to fuck. For a starters Bamber would just say he would be killing the family, at a push mention his methods. She says stuff like " how he would say goodnight to everybody " Bamber wouldn't say that. It's an add on by Julie or perhaps EP.
Also he
The excellent memory for dates. She would simply just say " he's been talking about it for a while, her recalling Xmas 84 and January 85 whilst maintaining a heavy schedule in her own life and at the same time being " flippant " of what Bamber is saying doesn't reflect the true picture she'd be able to recollect precise dates. Nobody would. Everyone is too wrapped up in their own affairs. Me, you, Mr Jones at number 10. Accept it may have come at prompting from the coppers. But it's not a true picture of what Julie is remembering.