Ina-Doris Warrick was stabbed to death in her North Ringwood home on Friday, March 21, 1986, after having dinner with hospital orderly Colin Earl Graham.

There has been little publicity about her death since the 1980s, but Victorian cold case detectives will reveal on television series Million Dollar Cold Case on Wednesday night that Mr Graham, who remains a person of interest in the Warrick case, was jailed for at least 13 years for the murder of 21-year-old Hilary Stevens.

The then 43-year-old Mr Graham stabbed Ms Stevens four times in her back at her Wheelers Hill home after taking her out for dinner in October 1999.

Thirteen years earlier, in 1986, he'd also taken Ms Warrick out for dinner on the night she died.

He told police he dropped her home about 8.45pm, but denied any involvement in her death. Mr Graham, now 62 and living in the east of Victoria, was the last person known to have seen Ms Warrick alive.

Mr Graham, who was released from prison in February 2013, continues to maintain that he played no part in Ms Warrick's murder.

An autopsy revealed the nurse died from multiple stab wounds soon after having dinner and, police say, within five minutes of being dropped home.

"Both Hilary Stevens and Ina-doris died in similar circumstances," Detective Senior Constable Steve Kelly, the current investigator, told Channel 7.

"However, without a clear motive and without a weapon [or] any strong evidence makes it extremely difficult to solve."

Ms Warrick, a nurse, as due to start her first nightshift at Heidelberg hospital. She had taken time off after her husband died of cancer the year before and after undergoing major surgery.

A former champion gymnast, Ms Warrick was a triple certificate nurse who'd worked in emergency at the Box Hill hospital.

Her body was discovered on her bed by her lover, Dr Greg Stewart, on Sunday, March 23. Ms Warrick was still wearing the clothes the married doctor last saw her in two days earlier.

Dr Stewart also remains a person of interest in the investigation.

He changed his statement three days after his initial interview, revealing he'd discovered her body on the Sunday night, but panicked and fled, failing to ring police.

Her neighbour found her body on her bed the next day and phoned police.

Dr Stewart told Fairfax Media he still couldn't account for his "shameful" actions.

"There is no excuse other than my own mental state," he said.

"To not have reported what I saw and knew on Sunday and to have allowed someone else to have to do it. It's irrational

Dr Stewart, who denies any involvement in Ms Warrick's death said he met the young nurse when they were working at Box Hill hospital together and it was after the death of her husband that the pair's romantic relationship began.

"She loved her job and worked incredibly well at it. She was just brilliant ... If you were someone that loved her and someone loved by her, it was just fabulous," he said.

He said he had decided to leave his wife for her the night before she was murdered.

"Closure is a funny word that people use, I don't understand that ... it lives with you no matter what. It's just that justice needs to be done," he said.

A $1m-dollar reward is being offered to anyone who has information that leads to the conviction of Ms Warrick's killer.

If you have information, you can phone Crime Stoppers anonymously on 1800 333 000 or ask to speak with a cold-case investigator. Confidential reports can also be submitted to crimestoppersvic.com.au.

Million Dollar Cold Case screens on Channel 7, 9pm Wednesday.