Some twenty years ago I was part-owner of some sheep kept in a remote grazing area. Seem irrelevant ? Well, one day I visited them and found a young sheep that had caught itself in barbed wire and was injured beyond recovery. I decided to put it out of its misery. My penknife was not a suitable instrument for the slaughter so I was reduced to strangling it. I can therefore speak as being, in a certain sense, an experienced strangler. Don't read on if you're squeamish, but then you wouldn't be on this thread anyway if you were squeamish.
Of course I knew nothing about how to strangle, nothing about constricting key blood vessels to the brain etc. I set out to compress the windpipe and produce death by asphyxiation. Well, here is what I found : first, if you don't squeeze very hard indeed, the "victim" can still gasp. After very prolonged, very tight squeezing, calling for all my physical strength, the animal eventually went limp. I released my grip, and it promptly started breathing and struggling again! Renewed attempt, finally putting poor creature out of its misery, albeit at the issue of several very unpleasant minutes.
I now know that there is another way to strangle, for the real connoisseur. You have to get your fingers in the right place to cut off the blood supply to the brain. Death will be much quicker and less physical force will theoretically be required.
I take it that the pathologist is unwilling to state formally that the strangulation of Joanna was very protracted because the latter option may have been part of the deal. However, given that the windpipe of a living, struggling person, was crushed, it seems plain to me that we are not talking about a practically instantaneous death by simply cutting off oxygen to the brain. Even if he struck lucky, so to speak, as to where he put his fingers, he couldn't instantaneously crush the windpipe of a conscious unwilling victim. And even if theoretically she died of oxygen deprivation before he had finished crushing her throat, the fact that he continued to do so still seems quite incompatible with any intention except that of ensuring that she was dead.
I wonder if the prosecution might call a different expert witness as to the length of the strangulation process. The home office pathologist is the expert on Joanna's body. He is not necessarily the world's greatest expert on strangulation.