"Some people would draw a line in the sand and move on, but I have always had this view, the answer is always in the file," Iddles told the ABC.
The morning Maria was killed
The morning Maria was murdered, she eerily said to her oldest son Mark if anything happened to her he had to look after his younger brother Adam.
After her sons went to school she bought a cake, as if she was expecting company at the bookshop. She called her ex-husband John James about 11.30am but he was out of the office.
He called her back in a phone call that would later play a crucial part in the murder investigation.
As they were talking Maria told her ex-husband to hold on and put the phone down.
"I then held on and while doing this I heard discussion in the background and then a bit of a scream and then there was more discussion and then silence," he said in a police statement.
"I then started to get edgy and started to whistle into the phone to attract someone's attention.
"I could then still hear the conversation in the background and I couldn't hear the exact words, but Maria was talking fairly loudly.
"I then heard a second scream. I then really thought something was wrong so I decided to go to the shop to see what was up."
Maria James answered this telephone but never hung it up.
If the customer had been there two minutes earlier, she would have seen the killer fleeing the building.
There were two witnesses who believe they saw the killer on that wintry afternoon.
A lady driving along High Street outside the bookshop slammed on her brakes as she almost hit the man running across the street.
Another man working on a nearby railway line saw him running too, and described him to police as 170cm and chubby with hairy arms and a receding hairline. He was in his late 30s or early 40s.
Police handed out posters of an image but a number of people who knew Maria could have fit the description.
The Thornbury bookshop where Maria James was murdered on June 17, 1980. Photo / News Corp
Suspects and love affairs
"I've investigated over 320 homicides and those with multiple stab wounds like this, I don't think I've ever charged anyone where there was no connection between the killer and the deceased," Iddles told the podcast.
In Maria's home were two cups of coffee, and Iddles believes she was with somebody she felt comfortable with.
Iddles said it was likely Maria was attacked from behind because there were no wounds on her arms that suggested self defence.
"My guess is she was making her way to the bedroom where she knew there was a lock on the door. The person responsible has grabbed the knife, which is really a weapon of opportunity," he said.
"The person who did this did not go there with an intention to kill her. They followed her to the bedroom where she's been attacked and eventually tied up. I think her hands would have been tied up after she was stabbed."
Those close to her were quizzed about whether she had any arguments with men and her son said police were pointed towards a real estate agent.
Her son Mark told the ABC there had been a sexual relationship between Maria and the agent and his mother was upset she didn't know he was married.
Police ruled him out as a suspect after they checked out his alibi.
Another suspicious person was a neighbour named Mario. He was a loner who lived with his mother.
The morning of her murder, Mario was standing at Maria's front door with a briefcase.
He was trying to sell the magazines to Maria.
Iddles said when police questioned him he admitted they had an argument about her not taking the magazines but he left.
Later when police searched his home, they found some green twine holding up tomatoes in the backyard. It appeared to be the same twine as that wrapped about Maria's hands.
Police also found a dry cleaning receipt that suggested the day after the murder Mario drove a far distance to have his pants dry-cleaned. On the receipt the dry cleaner had written there was a stain similar to blood.
Iddles had found blood on a pillow that didn't belong to Maria, and tracked down Mario in 2001 at a retirement home to get a DNA sample to see if it matched.
It didn't, and Iddles hit another dead end as he was ruled out as a suspect.
There was another potential love interest in Maria's life who police questioned.
He told police he would visit the bookshop but there was no deeper relationship and he denied involvement.
But in a dramatic twist, two days after police questioned him, he committed suicide.
It raised police suspicion but it was not known if he was already suffering from a mental health issue. He left a note mentioning the homicide squad but it wasn't a confession.
"Why would he commit suicide two days after being interviewed? Was he worried he was going to be caught, or was he a person already suffering from some mental illness?" Iddles said.
Police attention then turned to the church up the road and Father Anthony Bongiorno.
He made wild claims Maria was a sex worker, running the business from her bookshop.
Police drawing of the murder suspect.
The bloodied priest
According to the ABC, police obtained a new clue in 2013.
A family friend visited Maria's son and was very suspicious of the local parish priest.
Maria was a churchgoer and the ABC reports her 11-year-old son Adam, who had Tourette syndrome and cerebral palsy, told her he had been sexually abused by Father Bongiorno.
The day of her murder, Adam heard his mother on the phone, upset and angry.
The ABC reports that Father Bongiorno was moved from the church in Thornbury to St Ambrose in Brunswick.
He allegedly abused three boys there and was charged in 1996.
Father Bongiorno was acquitted of two of the accusations and the third case was discontinued. He died in 2002.
Father Bongiorno always said he was in a meeting with another priest during the murder but police were suspicious after a man working on the electricity box at the church the day of the murder saw him run back to the church all bloodied.
"A chap that I recognised as the person in the paper, Bongiorno, came on the left hand side and I looked at him from about eight metres away," Allan Hircoe told the ABC.
"He had blood on one side of his face, and one of his sleeves was rolled up and he had blood on that arm."
Hircoe approached the priest, who said he cut his face on a wire fence.
Hircoe went to get a first aid kit but when he returned Father Bongiorno was nowhere to be seen.
In 2015, Father Bongiorno was eliminated from the suspect list on the basis of DNA evidence.
"While I understand he may have been ruled out on DNA, I don't know where that sample came from," Iddles told ABC.
