This Sunday 7News Spotlight speaks exclusively to an Aussie mum accused of the unthinkable.

Did Lisa Cunningham kill her seven-year-old stepdaughter Sanaa, or was her death a medical tragedy?

In her first on-camera interview, Cunningham speaks candidly from inside a maximum-security prison in Arizona about the devastation of losing her family and the impact of eight years' incarceration without trial.

Lisa said, "It's always been such a mystery to us why it is easier to believe that we tried to slowly kill her with this bizarre, delayed death torture story than it is to simply accept the fact that she entered into the early onset period of serious mental illness."

The alleged killer details the final 10 months of her stepdaughter's life, a time in which prosecutors claim she and her husband, Germayne, subjected Sanaa to abuse that ultimately caused her death.

The exclusive story also features never-before-seen family videos and text messages that prosecutors claim prove their case, texts that Lisa says don't tell the full story.

"If you look at our lives from a distance and you go through our messages and the way we communicated with each other, you are going to form your own opinions," Lisa said.

Reporter Ashlee Mullany said: "The story of Lisa Cunningham is confronting whichever way you look at it. This is either a case of an Australian mother accused of an unthinkable crime, or a woman unjustly stripped of her freedom, family and voice for eight years.

"I covered Lisa's first court appearance after her arrest in Arizona almost a decade ago and what should have been her temporary holding cell has become her home for all these years, without conviction. The wheels of justice turn slowly, but this has been an agonisingly long wait for answers.

"Lisa is adamant she has nothing to hide and wants to share her story with Australia."

7News Spotlight on Sunday investigates how critical defence infrastructure is alarmingly exposed.

What happens around a warship docked at a major tourist hotspot will shock viewers and raise urgent questions about our national security.

The investigation spans key military sites including Pine Gap, Williamtown RAAF Base, Amberley RAAF Base and Garden Island Naval Base, where billions of dollars in defence assets are housed.

What's exposed are weaknesses in the protection of critical weapons systems: F-35A stealth fighters stored under shade cloth and naval ships and our most important air bases subject to easy intrusion.

Liam Bartlett said: "We found billion-dollar fighter jets stored under shade cloth, warships exposed to drones, and critical bases protected by little more than cyclone fencing. These are critical gaps in our defence capability at a time when our adversaries and neighbours are investing like never before."

Speaking to 7NEWS Spotlight, former Chief of Army Peter Leahy, alongside key military experts and industry insiders, warn that Australia's defence policy may be woefully inadequate for the real-world threats we face.

Lieutenant General (ret) Peter Leahy told Liam Bartlett: "This peace is fast coming to a close, so we better be ready for war. And I don't think we're ready."

Bartlett also travels to the Philippines, to witness how other nations are standing up to China's military aggression now, while Australia's defence plan will not see us combat ready until at least 2030.

Liam Bartlett said: "Our investigation shows that while the threats are evolving rapidly, Australia's response is stuck in slow motion. We're investing in submarines we won't see for a decade, while our current defences are exposed and under-equipped."

In the Philippines, Bartlett catches up with Defence Minister Richard Marles, who has been dodging 7NEW Spotlight's questions for months, to discuss a policy experts say is all words and no action.

"You don't want to be known as minister for show bags," Bartlett said. "There has to be substance to it."