Police say the double fatal house fire in Dunedin last week is now a suspected double homicide.

In a release this morning, Detective Inspector Steve Wood said the suspicious fire at 66B Wesley Street in South Dunedin likely did not cause the deaths of David Ian Clarke and Anastasia Margaret Neve.

Investigators and forensic experts now believe the pair were dead before the fire began.

Autopsies have now been completed and the bodies of the two have been returned to their families.

Police say a 46-year-old man will appear at Dunedin District Court today charged with arson, but said no one has yet been charged over the deaths at this time.

They said this is a complex investigation which is complicated by the damage caused by the fire.

Considerable forensic data remains to be analysed, which police say will take several weeks.

"We still have a long way to go in order to establish the exact details around what occurred, but a team of detectives are continuing to work tirelessly on this case," Mr Wood said.

Police are interested in hearing from anyone who may have seen or heard something that could assist them with their investigation.