If the death of David Kelly corresponds to the "murder hypothesis" and the murder wasn't carried out at Harrowdown Hill, then some form of "abduction" needs to have happened, in my view.
One possibility to be considered is that David Kelly was abducted by individuals posing as Police officers.
There was a similar case in Scotland in 2006, Police reconstruct city abduction, where a witness in a trial was supposedly arrested by two supposed plain-clothes police officers. His skull was dragged up in a fishing net some considerable time later.
Returning to the David Kelly case, if a car had driven up beside him during his walk and two seeming Police officers were to have asked him to accompany them, then it's likely that he would not have resisted entering the vehicle.
Once in the vehicle the opportunities for escape would have been greatly reduced.
At the moment I offer this as a purely hypothetical scenario.
But it would provide an explanation of how David Kelly could disappear with no sign of a violent struggle.
If, hypothetically, David Kelly was handcuffed via the left wrist then friction there might explain the "vital reaction" observed by Dr. Nicholas Hunt in his postmortem report.
Many other "abduction" possibilities exist. I simply offer this one as an explanation which would be consistent with the evidence I'm aware of.