Even though the precious memory is 43 years old, his face is etched in her mind as firmly as if she saw him just yesterday.

And while the passage of time has eased the pain of losing her child, she still clings to the faint hope Jason may still be alive.

Precisely what happened to Jason Shannon and his whereabouts is one of SA’s most enduring, yet forgotten, mysteries.

He was snatched by his mentally-ill father John “Barry’’ Shannon during an access visit in June, 1973.

Mr Shannon, 26, died in a car smash two hours later — but there was no trace of 10-and-a-half-month-old Jason in the wreckage.

Police have just two theories to work with.

The first, and unfortunately most likely, is that Jason was killed by his father shortly after the baby was abducted from his grandparents’ Blackdown St, Elizabeth West, house at 7.15pm on Saturday, June 9, 1973.

His tiny body was most likely disposed of randomly. Adelaide was in the grip of a winter storm the night Jason was taken and he may have been thrown into a swollen river or drain in the mid-north region prior to the head-on car smash near Roseworthy that killed Mr Shannon. A logical assumption is that a guilt-ridden Mr Shannon committed suicide.

The second theory, which also lacks any solid evidence to support it, is that Jason was given to another person by Mr Shannon to care for and raise. If this is the case, Jason may well be alive today — oblivious to his traumatic past life and his real mother’s existence.

Jason’s mother Michelle, who is now 67, can still vividly remember the night Jason was taken from her parents’ home. She had been living there for several months after moving out of the matrimonial home following an incident in which Mr Shannon hit her.

“I can remember Barry came to the house twice that day, which was unusual,’’ she said.

“He came early afternoon and again in the evening.’’

Although the couple had separated and she had won custody of Jason, there were no restrictions on Mr Shannon’s visits. Besides the second visit that day, there was nothing about Mr Shannon’s behaviour that raised any suspicions about what he intended to do.

One minute Mr Shannon was sitting on a couch with Jason, then seconds later it was noticed both were missing. He was last seen driving off at speed with the headlights of his Wolseley sedan switched off.

While police were alerted, there was no sign of the vehicle until it was involved in a head-on smash on Main North Rd, about 1km south of Roseworthy, at 9.15pm — two hours after Jason was abducted. Over the ensuing days police conducted widespread searches, but failed to find any trace of Jason.

Michelle said her father, Alfred, never got over Jason’s abduction.

When Barry Shannon snatched Jason from the lounge, the baby’s grandfather ran out after him but could not catch him as the Wolseley sped away. He ran back to his own vehicle to give chase, but could not find Mr Shannon.

That played on dad’s memory for a long time afterwards,’’ Michelle said.

Heartbroken, Michelle left Adelaide with her parents and returned to the United Kingdom in early 1974, just over six months after losing Jason. She later remarried and has one son.

She remembers being “very mixed up’’ and feeling guilty about leaving Adelaide with her baby’s disappearance still unresolved.

“I immigrated to Australia to make a new life and I felt sad, very sad (to leave). I loved the people,’’ she said.

“People think you should just adapt, but you can’t. You don’t feel whole, if that makes sense. 
“There is a void, a hole, and it needs to be filled.’’

She remembers Jason as a happy baby who was never short of love, with her siblings always jockeying to nurse him or carry him around.

“It was many a year that every morning when I woke up my first thought was of Jason,’’ she said.

“One day, it was years after, I woke up and it was strange because he wasn’t the first thing I thought of. But there is not a day I don’t think of Jason.’’

Michelle visited Adelaide last November and was taken to the crash site where she laid flowers in memory of her former husband. She still mourns the husband she knew battled a mental illness.

Michelle said she desperately wanted to know what happened to Jason and still clung to a faint hope he could still be alive.

“I think any human being would have that hope,’’ she said. “I say a prayer every night and I talk to him during the day.’’

Major Crime case officer Detective Sergeant Cameron Georg said if Jason had been murdered and concealed by his father the chance of locating his remains was now “remote’’.

Soil samples taken from Mr Shannon’s shoes, the car pedals and mudguards suggested he had not been walking in dirt or mud or involved in any digging. It was consistent with him having been at his home address and his in-laws, and he was unlikely to have left a paved surface. This tended to indicate that he may have simply disposed of Jason’s body in a flowing creek or drain near a roadside.

Detective Sgt Georg said the two-hour window between the abduction and the car crash limited the distance Mr Shannon could have travelled to a rough circle covering Port Wakefield, Clare and Elizabeth.

“He simply didn’t have the time to go much further than that and then get back to the crash site near Roseworthy,’’ the detective said.

In 2005, detectives examined a report that a grave at the Church of Christ cemetery at Kapunda had been interfered with, but no conclusive connection could be made.

The alternative theory that Jason may have been given to a third person to raise was possible, but was not supported by any evidence.

Detectives have investigated if Mr Shannon’s parents or brother, who are now all deceased, left their estates to anyone unusual who matched Jason’s age profile, but this provided no leads.

Mr Shannon’s parents had funded his court battle with Michelle over custody of Jason and they were aware of her plans to move back to the UK with her parents.

Detectives are still investigating information Mr Shannon may have formed a close bond with a female patient at the Fullarton Private Hospital, where he was being treated for his mental illness in 1972.

“It is possible Jason could have been given to someone,’’ Detective Sgt Georg said.

“The paternal grandparents wanted Jason to stay with them. With this background maybe he had given the baby to a friend, relative or someone close to raise the baby as their own. If this was the case, we would very much like to hear from anyone who can shed any light on this.’’