Theo Hayez inquest traces missing backpacker's mobile phone trail up Cape Byron

This map shows the route that Theo Hayez took to Tallow Beach on the night he disappeared. (Supplied: NSW Coroners Court)

Evidence from a professor of telecommunications appears to back up a police theory that missing Belgian backpacker Theo Hayez tried to climb a steep slope near Cape Byron in the dark.

The 18-year-old was last seen leaving the Cheeky Monkeys bar around 11pm on May 31, 2019.

GPS data from Google shows him walking along Tallow Beach to an area known as Cosy Corner, at the base of Cape Byron, but the tracking stops just after midnight.

On Thursday a coronial inquest heard evidence from Aruna Seneviratne, a professor of telecommunications at the University of New South Wales.

He told the court Theo's phone had contact with towers in Byron Bay and Ballina on three occasions between 12:05am and 1:02am, allowing him to triangulate the signal and produce timing advance figures that showed the distance of the phone from the towers.

The court was told the figures were accurate to within 78 metres.

Relations of Belgian backpacker Theo Hayez previously told the inquest he was not a risk taker. (Supplied)

Did Theo try to climb the headland?

Professor Seneviratne told the court the figures showed Theo moving away from the Massinger Street tower in Byron Bay and onto the Cape Byron headland.

The inquest was shown this map, which estimates the movements of Theo Hayez using phone tower triangulation. (Supplied: NSW Coroners Court)

"I am highly confident that the phone has moved more into the headland area after five past midnight," he said.

"There is a high degree of confidence that [the phone] is not at Cosy Corner.

"My overall conclusion is in the green areas, rather than the yellow or blue areas in the same vicinity."

Professor Seneviratne told the court it was "not a precise science by any means",  he said he repeated his calculations 10 times.

Cosy Corner at Tallow Beach is the last place Theo Hayez is known to have been. (Supplied: NSW Coroners Court)

The court also heard that a police officer made the trek from Cosy Corner to the crest of Cape Byron in August last year while sending texts from the same brand of phone that Theo was using.

Professor Seneviratne told the inquest he was "highly confident" Theo's phone moved towards the headland after midnight. (Supplied: University of NSW)

Professor Seneviratne said the timing advance figures produced then were "similar, given the variations that you would expect".

The inquest heard from family members last year, who told the court they could not imagine Theo embarking on such a dangerous climb in the dark.

But today's evidence appears to add weight to the police theory that the teenager fell into the ocean and drowned while trying to scale the cliff.

Police believe he may have dropped his phone during the climb and fallen while trying to retrieve it.

The inquest heard evidence from its last witness today, with Coroner Teresa O'Sullivan expected to hand down her findings later this year.