The father of Kathleen Folbigg’s dead children has refused to provide DNA evidence to a lawyer ahead of an inquiry that will examine New South Wales’s worst case of serial filicide.

Volumes of medical and forensic evidence are being gathered before the 2019 inquiry that will examine whether four of the Folbigg children were killed by their mother in the decade from 1989 in the NSW Hunter Valley or potentially died of natural causes.

At the final directions hearing on Wednesday, former NSW district court chief judge Reginald Blanch – who’s heading the inquiry – said Craig Folbigg had refused to provide a DNA sample when approached by his former wife’s lawyer.

Folbigg filed a complaint with the Law Society of NSW about being contacted by his ex-partner’s legal team. There’s no suggestion he’s not cooperating with the inquiry.

Kathleen Folbigg has supplied a DNA sample from Silverwater correctional complex where she is serving a sentence for killing her children Caleb, Patrick, Sarah and Laura, who all died aged between 19 days and 19 months.

She was jailed in 2003 but the NSW government in August this year agreed to a judicial review of her convictions.

Her legal team has suggested “damning inferences” drawn from Folbigg’s own diary entries may be upended if new medical evidence suggests the children could have died from natural causes.

Blanch on Wednesday noted new medical evidence could be provided to the inquiry which “leads to the exculpation of Ms Folbigg”.

Counsel assisting Gail Furness SC on Wednesday suggested there could be three weeks of scientific and medical hearings before Kathleen Folbigg potentially gave evidence.

Hearings will begin in the first week of March and the inquiry is expected to run for six to 12 months.