The police officer in charge of the original investigation of the Lundy double homicide was told by an expert it should remain a mystery.

Inspector Ross Grantham has been on the stand in Mark Lundy's retrial for the murders of his wife and daughter.

UPDATED 6.40PM: Lundy's defence lawyer Ross Burns asked what neuropathologist Dr Heng Teo said about cells on a slide made from a stain on Lundy's polo shirt.

Mr Grantham says “Dr Teo looked at the slide, he returned it to me. He said that a man shouldn’t be convicted on the strength of one glass slide … and it should remain a mystery.”

Dr Teo said the cells on the slide were too degenerative to be tested.

Mr Burns also asked Inspector Grantham about potentially suspicious activity mentioned by neighbours of the Lundy’s - when canvassed by police following the murders.

Ross Burns says neighbours told police about a normally calm dog ‘nutting out’ at about 10pm on the night of August 29, as well as hearing a high pitched female cry that evening, and a next door neighbour hearing the sound of smashing glass.

Inspector Grantham says anything of significance would’ve been followed up.

Earlier the court heard Mark Lundy called a meeting with police to check up on the progress of the investigation into the deaths of his wife and daughter.

In December 2000 Lundy arranged a meeting with police through his lawyer.

Police asked if they could re-examine Lundy's car, and he agreed.

“I then said we’d also like the suit cover or case which he took his clothes to Wellington in to test as well, again the accused readily agreed,” Inspector Grantham says.

“I also asked to look at his tools, which he agreed to as well.”

Lundy told Ross Grantham him he wanted to help police in any way he could.

Earlier today – jurors heard a forensic expert who specialises in animal DNA found traces of sheep, beef and pig in slides taken from the stains on Lundy’s shirt.

Elizabeth Wictum says those traces were consistent with processed food, and could’ve got on the shirt through cooking.

She also said there was evidence of human DNA seen in the tests she carried out.