UPDATED 1.03PM: The Wellington jury in Mark Lundy's retrial for murder has retired to consider its verdict.

Justice France has finished summing up the case for jurors in Lundy’s retrial for the murders of his wife and daughter.

He’s referred to a man, known as Witness X, who says Lundy confessed while in prison.

Justice France says the jury should consider the likelihood of Lundy telling a stranger what he’d done.

"In these situations of an alleged one-off admission you need also to think about the motivations behind his giving evidence."

The Crown says X was offered nothing in return for his testimony.

Justice France said some of the theory of what happened in August 2000 has changed, but jurors should reach a verdict based on the evidence put forward in 2015.

"Remember it's not your job now to look at whether the police did it properly last time. It's not relevant to your task now whether mister Lundy should have been convicted that time."

Justice France said when assessing the information this time, jurors can consider the fact the prosecution changed its theory on when the murders happened.

Justice France also said the evidence of mileage and fuel usage in Lundy’s car is not exact science and Lundy’s defence team says the journey didn’t take place.

"If you accept that point then you should acquit because the trip would be impossible. If you don't accept it then you obviously move on to look at the other issues that are there."