Shandee’s story: Doubts cast over accuracy of GPS data

Location data from the taxi of a crucial witness at John Peros’s 2017 murder trial was presented as accurate ... but was it?

Shandee Blackburn Picture: Supplied

GPS location data from the taxi of a crucial witness at John Peros’s 2017 murder trial was presented as accurate despite some co-ordinates appearing inside nearby buildings.

The coordinates show taxi driver Jaspreet Pandher’s movements on the night of Shandee Blackburn’s 2013 slaying and were used by Mr Peros’s legal team to discredit the prosecution case that a running figure captured in CCTV footage was Blackburn’s assailant.

Mr Peros was acquitted by a jury in less than two hours. He denies involvement.

The data is examined in the latest episode of the investigative podcast series Shandee’s Story, which follows Mr Pandher’s movements on the night and reviews evidence not presented at the murder trial.

Mr Pandher witnessed Blackburn struggling with an assailant on a Mackay street corner in the headlights of his maxi taxi shortly after midnight.

He was performing a U-turn further up the street when he saw a male figure running across a grassy paddock away from the scene.

CCTV footage from a nearby residential premise corroborates Mr Pandher’s version with a running figure seen heading towards Blackburn and then away moments after the taxi driver drove past the murder location.

However, at trial Mr Peros’s defence said GPS time and location data from Mr Pandher’s taxi suggested the figure running in CCTV footage was already well out of his view when he made the U-turn.

In a separate but related argument Mr Peros’s defence said the running person in the footage didn’t have enough time to launch the frenzied knife attack because of the timings involved.

If the theory is correct Mr Pandher witnessed a second running person seconds and metres apart from the running figure in CCTV footage.

Mr Pandher’s taxicab contained a Mark IV TaxiCam security camera system which recorded still images according to six input triggers and embedded them with GPS time and location data.

The accuracy of the GPS data was not contested at the 2017 trial and jurors were told there was “no dispute” the coordinates were accurate.

However, a map of the GPS coordinates compiled by a police mapping unit and shown to jurors at the murder trial suggested some of the locations recorded that night were inside nearby buildings and therefore inaccurate.

The defence theory relied on accurate location information and a discrepancy of even a few metres could cast doubt on whether Mr Pandher was truly not able to see the running figure visible in CCTV footage.

The podcast episode also examines the witness statement of Guy Bridson, an electronics technologist who regularly inspected and assessed Mark IV TaxiCam systems at the time. Mr Bridson’s evidence, not presented at the murder trial, suggested the GPS coordinates could not be relied upon for pinpoint accuracy.

“The GPS location information is specific as accurate to 5 – 25 metres but typically 8 metres depending on the number of satellites available to the receiver,” Mr Bridson said.