Jan, in Jeremy's second interview, he said "There are many ways to get into the house, i.e. windows."
He was then asked "What do you mean, insecure windows?"
Jeremy replied "Insecure windows, secure windows, it makes no difference."
However, Jeremy was shortly afterwards asked to explain, and said "With sash windows you can flick the catch with any thin metal object and open the window, but you can't close them from the outside." Shortly afterwards, he said he couldn't have told Julie of the "banging on the window frame" method of securing a latch from the outside as he didn't know of that method.
Note that the kitchen didn't have a sash window. It's likely that all the other openable windows were sash windows. A sash window wouldn't be fitted above a sink, as it's very awkward to operate a sash window unless you can stand close to it, which the sink would prevent.
If Jeremy's "it makes no difference" comment was regarded as conceding that he could open the secured kitchen window from the outside, or secure it from the outside, it was taken out of context and misinterpreted.