Days before they were set to greet their great grandchildren for the first time, Maurice and Zoe Antill were found dead in their backyard.
They had been fatally stabbed in barely a week before Christmas 2020.
Mr Antill was 87. His wife - who used a walking frame - was 86.
They had recently celebrated their 65th wedding anniversary.
Investigations suggested they were killed at their home in Brisbane's southern suburbs by Raghe Mohamed Abdi, 22, who was later shot dead by police on the Logan Motorway south of the city while wielding a knife and yelling "Allahu Akbar".
At the time it was treated as a "terrorism event" by Queensland police, an inquest was told on Monday.
Abdi was being monitored by the Queensland joint counter-terrorism team after being released on bail for offences relating to an investigation into whether he was preparing to be involved in a foreign incursion.
But Detective Inspector Chris Knight on Monday told the inquest into their deaths that he believed the Antills were killed in a random attack by Abdi.
He said Abdi had left his family's home after an altercation with his stepmother on the afternoon of December 16 2020.
Det Insp Knight said hours later CCTV footage captured a "shadowy figure" in the Antills' backyard which he believed was Abdi.
He believed Abdi made a noise that made the Antills come outside and they were assaulted.
Det Insp Knight said he suspected Abdi then went inside, grabbed one of their knives from the kitchen and fatally stabbed the Antills.
Forensic tests found Abdi's fingerprints on the rear security door.
There was also a bloodstained fingerprint that matched Mr Antill and Abdi.
Abdi's clothing and footwear were found in the elderly couple's bin with Mrs Antill's blood on a shoe.
The clothing Abdi was wearing when he was shot was likely from the Antills' house, Det Insp Knight told the coroner.
Early the next morning police received reports of a man walking alongside the Logan Motorway.
CCTV footage showed Abdi walk along the busy highway for about 45 minutes before two officers approach.
Their body worn footage shows Abdi saying "leave me alone".
He then takes out a knife and repeatedly yells "Allahu Akbar" before moving toward police and is shot multiple times.
Abdi was found in possession of the Antills' car keys and a knife with the same brand as the one used by the elderly couple.
Later that afternoon the Antills' bodies were discovered during a welfare check.
Searches in nearby bushland found Mr Antill's wallet as well as Abdi's ankle monitor worn as part of his bail conditions.
The Antills would be remembered for their loving nature, their son Howard said in a statement at the inquest.
"The impact and sudden loss of Maurice and Zoe will be felt forever," he said.
"They will never meet their great grandchildren, a visit that had been planned for that week in December."
Det Insp Knight said as part of his investigation into the Antills' deaths he consulted terrorism expert Levi West of Charles Sturt University.
Mr West believed there was insufficient evidence to substantiate that the Antills' deaths were an act of terrorism, he said.
However, Mr West said the attempted stabbing of police was "likely at least in part to be ideologically motivated".
Fourteen witnesses will be heard at the inquest before coroner Stephanie Gallagher over three days.
