Warning: This story contains discussion of a potential suicide.
An expert says rope found at the scene where an Auckland eye surgeon's wife allegedly ended her life was too insecure to hold any weight.
Philip Polkinghorne has pleaded not guilty to murdering his wife, Pauline Hanna, at their home and staging the scene as a suicide.
Analyst Robert Chisnall was contacted by forensic scientists to examine rope found tied to balustrades at the top of a stairwell in the home Polkinghorne and Hanna shared.
Speaking in the High Court in Auckland via video link from Canada, Chisnall said the rope appeared "too long and too insecure to suspend any weight".
"The insecure tangles collapsed, allowing the un-knotted end to slide to the floor," he told Crown lawyer Brian Dickey.
Chisnall observed that after the slippage, additional slack was still available at both ends.
"Further, the loop knotted around the balustrade slipped down at some point when the tangles collapsed."
He was provided photographs and did his own replications of the scene which he said verified the rope's insecurity.
He used metal rods to replicate the balustrades, spacing them at different intervals to test the hold of both the rope and knot.
Questioned by Polkinghorne's defence, Ron Mansfield, KC, Chisnall said in some tests the knot completely unravelled.
Mansfield questioned Chinsall's credentials, as he did not possess any forensic or engineering qualifications. Chisnall said he had experience in ropes through teaching rock climbing, rescue, and rope access.
Surgical knots were not found on a rope at the scene where Hanna died.
When questioned by Mansfield, Chisnall said the knots were not sophisticated and could be tied by most people.
He agreed the type of knots on the rope could be enough to hold someone's weight if you tied enough of them.
Mansfield asked Chisnall if he had been informed of Polkinghorne's occupation.
Polkinghorne was a prominent ophthalmologist in Auckland. He retired after his wife's death.
Chisnall said he believed Polkinghorne was an eye surgeon.
Mansfield began to ask Chisnall about surgical knots.
"You would know that a surgeon is well-taught in relation to knot tying and for an experienced surgeon wouldn't it just become second nature..."
Justice Graham Lang then interjected.
Mansfield showed the jury animations of complex knots used by surgeons.
The trial continues.
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