The trial of murder accused Mark Lundy yesterday centred on whether his car could have made the Petone-Palmerston North journey on one tank of petrol.
The High Court at Palmerston North was told police had made the return trip from Petone to Palmerston North and used 75 litres to do so.
Lundy's Fairmont holds a maximum of 68 litres.
The Crown alleges Lundy drove the Fairmont from Petone to Palmerston North and back in less than three hours on August 29, 2000, to kill his wife Christine and daughter Amber in their home.
Detective Danny Johanson refused to accept a defence argument that the results showed Lundy could not have made the journeys on a single tank of fuel.
He said it could have been done with less aggressive driving.
Detective Johanson said he took a Fairmont Ghia identical to Lundy's car and filled it at the Naenae BP Overbridge service station - the same petrol station where Lundy topped up his car.
He took notes while Detective Tim Moffat drove the car around various places Lundy had visited in Lower Hutt and Wellington before driving on to the Wellington motorway.
Detective Moffat began a pattern of "erratic" driving, including heavy acceleration and braking for the run to Palmerston North.
The fuel used between the fill-up in Naenae and a top-up in Palmerston North was 35.35 litres for 215km.
The next run was Kelvin Grove to Petone and return by Detective Johanson and Detective Gary Milligan. The southbound trip was via Shannon, Levin and Hayward's Hill, the northbound via Ngauranga Gorge, Levin and Shannon.
They left at 7.07 pm and on arrival in Petone the trip meter recorded 150.2km in 1h 36m.
That included Detective Milligan's 513m walk from the Lundy home in Karamea Cres to Hillcrest Drive, where a vehicle similar to Lundy's was seen by a witness the night of the murders.
The return trip was 147km, covered in 1h 28m and using 40.6 litres of fuel.
Detective Johanson said the trip from Naenae to Palmerston North with Mr Moffat driving was "at speed". He did not think they would have gone over 140km/h.
The round trip with Detective Milligan driving the first leg was also at speed, but Detective Johanson said again they would not have been travelling over 140km/h.
Detective Johanson told Lundy's lawyer Steve Winter the three trips covered 512km on 75.95 litres of petrol.
He said that in spite of Lundy's car having a 68-litre tank, he did not accept the three journeys could not be done on one tankful.
"It could have been done in a more efficient manner," he said.
He denied that at the time of the tests he was aware "suspicion was turning towards Lundy".
Detective Johanson said he understood the tests were intended to eliminate Lundy from the investigation, on instructions from Detective Sergeant Ross Grantham, who was heading the homicide investigation.
He was asked if there was any attempt to travel north leaving Wellington at between 5.38 pm and 6 pm, about the time it was alleged Lundy did so.
Detective Johanson said it was considered safer to avoid heavy traffic times.
He accepted more traffic would slow progress.
"[But] if you pushed the car harder, threw caution to the wind, you could do it in that time."
He said the Petone-Palmerston North return trip with Detective Milligan took 3h 5m, including Detective Milligan's walk from the Lundy house to Hillcrest Drive.
Justice Anthony Ellis queried the difference in fuel consumption of about 17 litres per 100km for 215km, and then the return trip, which showed 13.5 litres per 100km.
Mr Johanson said he had no answer for the discrepancy.
Earlier, Mark Lundy's claim that petrol was stolen from his car was disputed by a Ford technical manager.
The New Zealand technical services manager for Ford, Glenn Smelt, told the court that Lundy's car was fitted with an anti-theft device in the tank filler.
He said tests by Ford showed that fuel could not be siphoned from the tank without breaking the anti-theft device. The device on Lundy's car was intact.
Mr Smelt said the car's fuel economy of 450km to 500km on a full tank would suffer if it was driven hard and erratically, probably to under 400km.
Australian Standard tests showed economy results of 13 litres per 100km for city driving and eight litres per 100km for highway driving.
Mr Smelt said many drivers could achieve that result, and he had done so himself.
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