Gda O'Connor also referred to Mr Scott's statement to gardaí in which the accused said that he thought he had driven over the hitch of a trailer.

The witness said it is difficult to understand how a person with working knowledge of the machinery would not recognise the difference between hitting a trailer and rolling over someone on the ground.

Defence counsel Paul Greene SC put it to the witness that some of his evidence was based on "conjecture" and questioned him about the effect that slopes in the yard where Ms Treacy died could have had on his findings.

Michael Scott (58) of Gortanumera, Portumna, Co Galway has pleaded not guilty to murdering Ms Treacy outside her home in Derryhiney, Portumna, Co Galway on April 27, 2018.

The prosecution case is that Mr Scott deliberately ran over Ms Treacy following a long-running dispute over land.

Mr Scott's lawyers have said her death was a tragic accident.

Gda O'Connor told prosecution counsel Dean Kelly SC that he is a collision investigator and carried out an examination of sightlines from the cabin of the teleporter, along with examinations of the surface of the yard where Ms Treacy's body was found, and the workings of the teleporter.

He was aware that in a voluntary interview given by Mr Scott to gardaí, the accused said that he thought he had struck a trailer but before he stopped to check for damage, he drove forward because he was concerned that the machine might roll on the yard surface.

Gda O'Connor said he found the yard to be relatively smooth and the slope to be no more than 2 degrees.

He said it was "questionable whether a machine could roll on a yard with such a negligible slope".

The handbrake was not working but if the driver wanted to prevent the teleporter from moving they could leave it in gear or use the boom as an anchor, he said.

Gda O'Connor knew that Mr Scott had said he was most likely driving in second gear.

Testing showed that the maximum speed in second gear was 8 km/hour or 2.2 metres per second.

The distance from the shed where Mr Scott said the teleporter had been parked to where Ms Treacy's body was found was about 24 metres so he would have been driving for about ten seconds prior to the collision, the witness said.

Gda O'Connor described that as a "relatively long time to be reversing such a vehicle without looking around to check whether the yard was clear".

He also formed the view that it was "not plausible that a driver of such a vehicle would reverse 24 metres without looking physically to the rear".

Gda O'Connor was aware that Mr Scott had told gardaí that he may have been looking over his right shoulder but Gda O'Connor thought the most natural way to reverse the teleporter would have been to look over the left shoulder.

There was a large blind area created by the boom to the right and the engine to the rear.

He said it would be unusual to reverse using the one available mirror on the right of the vehicle which was partially obscured by the boom.

He said Ms Treacy's age and mobility issues meant it was "unlikely she could have just appeared at the point where her body was found".

He said that had the driver checked by turning his head to look through the rear window, "he would and should have observed Ms Treacy".

He measured the distance from her back door to where she was found at 45 metres and observed that due to the speed of her movement, she "would have been observable moving across the yard".

Gda O'Connor also formed the view that the tyre marks on Ms Treacy's body showed two distinct tracks, one from the right leg, across the back to the left hand.

He said there was a change in direction of the vehicle over the body from the left shoulder towards the left leg. He could not say in what order the tracks were made.

The most likely point of impact with the teleporter was at the rear left wheel where bodily fluid and tissue were found, the garda said.

Despite the dirt of the windows, Gda O'Connor found that the cabin allowed good visibility to the left and rear left side.

While he found that there was a significant blind spot to the right and rear of the vehicle when a mannequin was placed lying on the ground, there were no blind spots to the left and rear left.

He considered Mr Scott's statement to gardaí that he thought he had driven over the hitch of a trailer that was positioned less than one metre from where Ms Treacy's body was found.

Gda O'Connor said it would not be possible for the teleporter to roll over the hitch as it was 48cm above the ground.

He added: "It is difficult to understand how a person with working knowledge of the machinery would think that they rolled over a hitch 0.48 metres off the ground and not recognise the difference between hitting something such as that and rolling over someone on the ground."

The trailer, he said, had no brake attached and would move backwards if struck.

Gda O'Connor also noted that the window was missing above the cabin door.

If a pedestrian were placed between the front and rear wheels on that side, he said they would be "easily seen" by the driver.

Paul Greene SC, for the defence, told Gda O'Connor that he would characterise parts of his evidence as "conjecture" and "making assumptions".

Mr Greene put it to him that his suggestion that the driver would have seen a pedestrian between the wheels on the left side was based on the assumption that the driver looked to the left at that moment.

The witness agreed that he was not saying the driver looked to the left at that moment but that if he looked to the left he would have seen Ms Treacy.

He said it was an assumption "in part" and was based on the position of the body relative to the rear left wheel.

Gda O'Connor said his examination of the teleporter and its sightlines took place at a yard close to where the teleporter was removed for forensic examination.

He said he didn't know what the gradient was at the test yard but said to the eye it was a flat surface without any severe undulations, potholes or slopes.
He agreed that he had not measured the gradient at the test yard and that it had a tarmac surface while the surface at Derryhiney was concrete.

Mr Greene asked whether a change in gradient between Derryhiney and the test yard would have an effect on his findings. Gda O'Connor said it would not unless the difference in gradient were severe.

He said he had not observed a slope of 6.5 degrees close to Ms Treacy's remains but he could check if required.

He said he also did not note a large rectangular depression in the centre of the yard where an oil tanker had previously been placed.

He said he also had no note of abrupt edges to that depression.

When he walked around the yard, he said he didn't notice any severe depressions.

Mr Greene put it to him that it was not "the smooth yard you say it is".

Gda O'Connor said that he had not said it was "pristine" but that it was "relatively smooth" compared with other farmyards he had attended.

The evidence continues tomorrow in front of Ms Justice Caroline Biggs and a jury of eight men and seven women.