A killer narcissist who almost got away with murder was brought undone by his own arrogance, according to the rebel cop who brought him down.

Gerry Thornton, who was heading up an outback police station in south-west Queensland at the time, disobeyed orders to pursue a murder conviction for a former officer who claimed his partner died in a freak accident.

“It just It looked staged to me,” Thornton said of the 2009 death of 36-year-old Lainie Coldwell.

At the murder trial of her killer Louis Mahony, the court heard the former Northern Territory constable bashed Coldwell in the back of the head with an iron at their home in Charleville.

Mahony then moved her body to the base of a large gum tree, claiming she’d fell out of the tree while taking down Christmas lights.

“I went to the police station and there was no CIB (Criminal Investigation Bureau) there, and I said to a uniform fellow: ‘You better tell him to check this out, check the insurance out, because that didn’t happen like he’s saying. And then nothing happened’.” Thornton said.

With no support from QPS, Thornton teamed up with the insurance company Westpac Life, which was investigating Mahony for insurance fraud.

There were multiple insurance policies totalling $2.25 million.

“There was never any doubt he was responsible because there were only three people there that day — the daughter, Lainie and Louis. There was no way in the world she (Lainie) was ever in that tree,” Thornton said.

Louis Mahony is the second killer narcissist to be analysed in 7NEWS’ hit new podcast/vodcast Kiss & Kill – the first being Gerard-Baden Clay.

Forensic criminologist Claire Ferguson, who features in the podcast, said Mahony tried to come across as a lovable larrikin, but was “much more calculating” than that.

“It’s interesting, right – because what we know about [intimate partner homicides], especially the ones that are concealed, like this case and like Gerard Baden-Clay and [Borce] Ristevski, is that they don’t actually do a lot of stuff to the evidence,” Ferguson said.

“They don’t manipulate that much evidence. They manipulate people, and they’re really good at that.”

Kiss & Kill is a deep-dive on the behaviours, patterns of behaviour and psychopathy of killer narcissists and/or expert abusers.

It also explores claims that so-called ‘crimes of passion’ are a ‘load of rubbish’.

Thornton said Mahony was caught because he “overestimated his ability”.

“He kept tripping up because he thought he was invincible,” Thornton concluded. “And you’ve got to admit, those first few months, he had a pretty good run. No one questioned him. So his confidence is sky high. And I think he was a little bit disappointed that people didn’t recognise sort of what a good job he’d done.”

For all the latest, head to 7news.com.au/kissandkill

Kiss and Kill is available across Seven’s full suite of broadcast, digital and audio platforms, with exclusive investigations on 7NEWS at 6 and the full vodcast available at 7plus, on LISTNR or wherever you get your podcasts.