Evidence that police say shows Michael McGrath driving to a mate’s place where he was allegedly shot dead has today been rubbished by an expert defence witness.

Former detective David Horsburgh reviewed hours of crucial CCTV footage that has formed a crucial plank in the murder case against ex-prison officer David Benbow.

The Crown alleges that Benbow, 54, lured his builder friend McGrath to his Candys Rd home at 9am on May 22, 2017, to help him move some heavy railway sleepers.

It says Benbow shot him dead before attending a counselling session in the city at 10.15am and later dumping his body, which has never been found.

The jury trial at the High Court in Christchurch, which is nearing the end of its sixth week, has heard evidence that the Crown says shows McGrath driving in his dark blue 1994 Subaru Legacy station wagon on Wales St at 8.54am that day – allegedly on his way to Benbow’s.

Other footage from the local Halswell New World supermarket purportedly showed him driving past again a minute later.

But today, licensed security consultant Horsburgh cast his doubt over the footage while being led by defence counsel Kirsten Gray.

The Wales St footage at 8.54am shows McGrath’s dark blue car with its distinctive non-factory RFRB (Run Fast, Run Beautiful) grill – a Japanese after-market accessory - and headlights, police officers have told the court.

David Benbow has pleaded not guilty and is on trial at the Christchurch High Court for murdering Michael McGrath in 2017. Photo / George Heard

Horsburgh, however who describes himself as a forensic video analyst, said the camera angle doesn’t give a clear view of the front grill while its resolution is “very poor”, making it “very difficult to minutely examine the vehicle for differences in the nature of the grill design”.

“There is not enough information there to draw that conclusion,” he said.

Asked about the car’s colour, Horsburgh found it was “a dirty brown – it’s not blue”. He also disagreed with police who said the car featured a black cap in the centre of the mag wheels like McGrath’s car had.

The defence witness also called police conclusions over the supermarket footage as “completely inaccurate and unreliable”.

Although the cameras were high-quality, the car is shown 156m away and “using identification standards it falls enormously well short of any image resolution within that to identify anything at that distance”.

While he agreed the car was dark in colour and “possibly blue”, there was not enough information in the pixels to be certain it was blue.

During cross-examination, Crown prosecutor Barnaby Hawes questioned Horsburgh’s forensic video analyst qualifications and said he found it “odd” that he hadn’t played any raw footage today during his evidence.

The cross-examination will continue this afternoon.

Benbow’s lawyers earlier warned the jury of “investigative bias” and “tunnel vision” from police early in its investigations who they claim were trying to find evidence to support their case.

Christchurch builder Michael Craig McGrath, 49, was last seen at his home in Halswell, Christchurch, in May 2017.

While the Crown accepts there is no body, no murder weapon, and little forensic evidence in the case, it says there is a strong circumstantial case consisting of many threads that, when taken together, show Benbow is guilty of McGrath’s murder beyond reasonable doubt.

The trial, before Justice Jonathan Eaton, continues.