Gus Lamont’s devastated dad has broken down in tears while pleading for help to find his little boy, almost a year after the four-year-old vanished without a trace from a remote South Australian sheep station.

“We miss Gus more than we can describe,” Joshua Lamont said through tears in an emotional video message released on Wednesday.

“We are desperate to have him return home to us and we are desperate for answers.

“We believe that someone knows something. Someone knows what happened to Gus and may even know where he is.”

Sitting alongside Gus’s mum Jessica, Mr Lamont struggled to contain his emotions as the intensely private parents made a rare public appeal just days before the first anniversary of their son’s disappearance.

“Even if you’re feeling scared or unsure, if you know anything at all, we are imploring you to help us,” Ms Murray said.

“Even the smallest detail could be helpful.

“Please come forward and cooperate with police.”

Mr Lamont, visibly overcome, added a final desperate plea: “Please.”

The heartbreaking appeal came as the South Australian Government announced a record $1 million reward for information leading to the recovery of Gus’s remains or the conviction of the person or people responsible for his disappearance.

In another potentially significant development, police revealed “anomalies” had been identified in aerial images of Oak Park Station and were being reviewed by detectives.

The findings could result in police returning to the 60,000-hectare property for yet another search.

Gus disappeared from his grandparents’ Oak Park Station, near Yunta, on September 27 last year after he was last seen playing outside the homestead, just before dusk.

Despite the largest and one of the most intensive missing-person searches ever undertaken by SA Police, no trace of Gus has been found.

Premier Peter Malinauskas said the $1 million reward — the largest ever offered in the state — was approved after police approached the government in recent weeks.

“Justice needs to be done here, one way or another,” he said.

“We send a crystal-clear signal to anyone in the community that if you know something, you’ve got to speak.

Police Minister Michael Brown was equally blunt.

“Gus wasn’t just plucked out of nowhere and disappeared,” he said.

“Someone knows something and so I urge them to tell the authorities and to spare his family the pain that they’re currently going through.”

Major Crime Investigation Branch officer-in-charge Detective Superintendent Darren Fielke said the reward was an important new strategy in the investigation.

“There’s a missing four-year-old child. There’s a $1 million reward on the table. That’s what the fact of the matter is,” he said.

Det-Supt Fielke said police had requested the reward from the State Government in recent weeks, describing it as a legitimate investigative strategy rather than a sign detectives had run out of options.

“You’d understand that we don’t just ask for a reward after one week of investigation,” he said.

Police have conducted 11 ground searches over the past year, involving hundreds of police, specialist officers, emergency workers, Australian Defence Force personnel, Aboriginal trackers and volunteers.

Aerial searches involving Polair, drones and aircraft fitted with specialist cameras have scoured more than 700sqkm.

Det-Supt Fielke revealed Task Force Horizon investigators had recently completed a “painstaking, methodical, forensically detailed” manual examination of the aerial imagery, in addition to previous artificial intelligence analysis.

“As a result of that manual searching, we have identified some anomalies in the imagery that has been provided to us,” he said.

“These anomalies are now being further reviewed and, depending on how that review plays out, will determine whether we return to Oak Park Station and conduct further searching.”

He refused to reveal what the anomalies were.

“They’re interesting enough for us to have a look at,” he said.

“I’m not speculating on what they are, but we’ll have a look at them.”

Gus’s disappearance was declared a major crime in February as investigators increasingly focused on the possibility someone known to him was involved in his disappearance and suspected death.

Police initially investigated three main possibilities – that Gus wandered away and became lost, was abducted by a stranger, or that someone known to him was involved.

Det-Supt Fielke said on Wednesday the first two scenarios remained unlikely.

“So far, we have no evidence to support those theories, despite consistent and exhaustive investigative efforts,” he said.

“The focus of Task Force Horizon remains on the third scenario, and that is that someone known to Gus has been involved in his disappearance and suspected death.

“As you’re aware, I previously stated that one of the grandparents is a suspect in our investigation. That has not changed.”

Police have never publicly identified which grandparent is the suspect.

However, Gus’s grandmother Josie Murray publicly identified herself as the focus of the investigation in an exclusive 7News Spotlight interview earlier this year and strongly denied any involvement.

“They’ve said they don’t think I’ve hurt him, they think that I’ve buried him – that’s one of the theories they’re working on,” she said.

“For so many reasons it’s ludicrous. It doesn’t make sense. Why would you do that to yourself?”

Ms Murray has argued Gus may have been abducted and this week revealed the family planned to search wedge-tailed eagle nests around the property.

“The eagle aspect should be looked at,” she said.

“I mean, that is certainly, it’s highly unlikely, but it’s not impossible.”

She also pleaded with police to stop treating her as a suspect, saying it was “enormously frustrating” to believe investigators were wasting time that could instead be spent establishing what happened to Gus.

Asked on Wednesday about the grandparent’s public criticism and theories, Det-Supt Fielke said he was “disappointed”.

“We’ve reviewed all of those interviews, all of those comments, all of those theories that are being espoused by the person you’re talking about,” he said.

“They have no investigative value.

“We can discount all of them. It’s nothing new. They’ve all been looked at.”

Det-Supt Fielke said detectives had spent countless hours pursuing information and theories before discounting them.

“Task Force Horizon investigators haven’t been sitting on their hands for 12 months,” he said.

“Every piece of electronic information that has come into our office has been examined with a fine-tooth comb.

“We’ve looked at crazy theories, crazy stories. We’ve discounted them all, and we don’t discount them because it’s too hard.”

He acknowledged it was “frustrating” to approach the first anniversary without finding Gus.

“They live and breathe this every day,” he said of his investigators.

“We’d love a result. We’d love a result for that little boy. We’d love a result for his family.”

Det-Supt Fielke said investigators were dealing with an “unusual environment” at Oak Park that presented challenges.

Police have also brought in investigators from interstate to review some of Task Force Horizon’s work as part of the “robustness” surrounding the investigation.

“We are going to continue to thoroughly and meticulously investigate the disappearance of Gus until we get a resolution,” Det-Supt Fielke said.

“We are focused and determined.”

In their recorded message, Gus’s parents described his disappearance as “the most devastating and inexplicable event we have ever experienced”.

“We love him more than words can convey and every single day without him has been incredibly difficult,” Ms Murray said.

“Our heartache only grows as time passes and an entire year without any answers is upon us.”

She remembered Gus as a “beautiful, sweet and unique little boy” who loved music, listening to stories and playing in the natural world.

In the year he has been missing, Gus should have celebrated his fifth birthday while his younger brother turned one.

“One of the most heartbreaking things is that Gus and his little brother will not grow up and share their lives together,” she said.

“Gus was adored by his little brother.”

Mr Lamont thanked the family and friends who had helped them endure the past year, along with the community members, SES volunteers, Australian Defence Force personnel and police who had searched for Gus.

“The love and support we’ve had from family and friends has been overwhelming,” he said.

“It has kept us going and helped us remain strong and hopeful for the future.”

Almost a year after Gus vanished, no one has been charged over his disappearance and his whereabouts remain unknown.

The Nightly has contacted Gus’s grandparents through their lawyers for comment.

Anyone with information is urged to contact Crime Stoppers on 1800 333 000. Information can be provided anonymously.