Crown prosecutor Ban Vanderkolk says the guilty verdict in the double murder trial of Mark Lundy shows the importance of circumstantial evidence.

Lundy's wife Christine and daughter Amber were found dead in their Palmerston North home on the morning of August 20, 2000.

Later the High Court at Palmerston North was told that spots of blood and brain tissue on a polo shirt owned by Lundy were linked by DNA to his wife and daughter.

It was this link that was essential to the prosecution case, Mr Vanderkolk told National Radio.

"Circumstantial evidence is very strong and powerful when a number of individual items are wound together," Mr Vanderkolk said.

" was always going to be a circumstantial case and I think this case demonstrates that people need to have no fear about circumstantial evidence," Mr Vanderkolk said.

It took the jury of six men and six women 6-1/2 hours to reach the unanimous decision, which was delivered at the court at 8.40pm last night.

"Before a jury will find an accused guilty of an offence there is a very high standard of proof which has to be reached and clearly the jury found it reached in this case," Mr Vanderkolk said.

He, along with the investigating team of police, were relieved at the verdict.

Other evidence centred on whether Lundy made a return trip to Palmerston North, to commit the murders, from Petone, where he was staying on a business trip.

The prosecution argued Lundy could have done the trip in 75 minutes at an average speed of no more than 120kmh.

Also, after a discrepancy in petrol levels was pointed out, Lundy had told police some had been stolen from his car. Two witnesses said this could not have happened.

The Crown alleged Lundy had rigged his home computer to show that it was turned off at 10.52pm on August 29, 2000. This was the time he was with a prostitute in Petone.

The Crown also raised Lundy's financial position, drawing attention to the pressures of a $2 million property deal and his business finances.