An inquest has hear that A Sydney father suspected of killing his family was having an affair with a teen.

At about 11am the day before she died, Sydney mum Maria Lutz topped up her phone credit.

Maria then called her own mum in Bogota, the capital of Colombia, where she had grown up. On a carefree Sunday in late spring, the pair chatted about the different birds in their gardens on opposite corners of the globe.

Maria’s husband Fernando Manrique was busy with his own chores that Sunday. Recently, he’d made multiple trips to Bunnings to buy all manner of hardware. Now, he was using the things he’d bought to connect two tanks of carbon monoxide, out of sight in the shed, to the home’s various bedrooms.

He was constructing a brutally effective death trap to kill his family.

About 16 hours after Maria put down the phone to her mother, probably some time before dawn, Manrique’s contraption sprang into action delivering a colourless, odourless but lethal dose of poison gas to the home in Davidson on the city’s north shore.

Maria likely died as she slept, as did her children Elisa, 12, and Martin, 11, known to all as “Tin”.

A probable murder-suicide, Manrique also perished, sprawled in the hallway of their single storey home.

Even Tequila, the family pet, succumbed. He was found at the foot of Tin’s bed.

At an inquest into the four deaths, a lawyer for the Manrique family dubbed the events, the “silent deaths in the night”.

But also at the inquest, it was described another way; as an “evil plan” hatched by a man in financial “dire straits” whose marriage was as good as over and was having an affair with a teenager in the Philippines. Manrique lied to his family and colleagues, and even managed to bluff his way past two major companies to commit murder.

More than two years after the deaths, a timeline has emerged of how the Manrique-Lutz family spent their final tragic days and hours.

The inquest held last week looked into the deaths of the four and how the father was able to, almost casually, get hold of huge amounts of deadly, pure carbon monoxide and have it delivered to a residential home.

Tragically, while the family was struggling financially, Maria was about to come into money. Enough, perhaps, to start her life over.

For four days this week, a band of Maria’s closest friends made the trek to the coroner’s court in the city’s west to observe the inquest.

They were all mums of students at St Lucy’s Wahroonga, a school for children with intellectual disabilities. Sarina Marchi arranged a clutch of pictures created by Elisa and Tin around the courtroom.

One was a striking image of singer Jason Derulo, head cocked to one side. The pop star was Elisa’s favourite performer, Sarina said.

The young girl was so talented, her mum Maria had told Sarina, that she hoped she might become a graphic designer.

“They really are quite extraordinary given their ages,” coroner Elaine Truscott said. “Astounding really.”

BEGINS TO UNRAVEL

Maria met the man who would become her husband as a teenager in Colombia. By the time the couple moved to Australia, she was a successful lawyer and he worked in adverting.

Elisa and Tin were born in 2005 and 2006 respectively. Both were diagnosed with autism when they were three, leading Maria to give up work to care for them.

Manrique worked for multinational Fuji Xerox with his wage of more than $300,000 a year enough to support the four of them. But things began to unravel he was made redundant.

He took on a role with IT firm Drake Business Services. The job saw him travel to the Philippines where the company was expanding. But by 2016, Drake had still not broken even and with Manrique having a 10 per cent stake in the firm, it was impacting the family’s finances.

The inquest heard Manrique owed $28,000 on a credit card, the pair owed the Australian Taxation Office about $20,000 and the family trust contained just $6.

Detective Sargent Tim Pooley, who led the investigation, put it plainly: “They were in financial dire straits. He had massive tax issues, a credit card that was maxed out and two home loans reduced to interest only payments.”

PHILIPPINES ‘HOOK UPS’

The couple’s relationship was also disintegrating. The inquest heard Manrique confided in a friend that his marriage was “strained” and he would “hook up” with other woman in the Philippines.

One of those woman, the court heard, was named Jamielyn. Just 17 years old, Manrique met her in 2015 in a bar on Burgos Street, a seedy strip of strip clubs and massage parlours in Manila.

Jamie, as she was known, told police that the relationship eventually progressed to the point he promised to support her and buy her a house. He didn’t.

On a final trip to the Philippines in September 2016, Jamie noted Manrique seemed “particularly stressed”.

As for Maria, she had told her friends she and Manrique were sleeping in different rooms and hadn’t had sex since 2014.

In 2016, she told Manrique she wanted a divorce but if he shaped up she would consider giving him another chance.

This also didn’t happen. Maria found out about Jamie and was exasperated that, even when he was at home, he was little help with the kids. Eventually, she asked him to move out.

‘FATHER OF THE YEAR’

Days later on Sunday 2 October, two weeks before the deaths, Manrique asked to move back temporarily while he found somewhere new to live.

Something miraculous occurred, Maria told her friend Nichole Brimble — he was a changed man.

“He was good at home and Maria said if he’d been like this throughout their marriage she would never have told him to go,” Mr Casselden said .

“During that week, Maria described him as ‘father of the year’.”

In reality, he was as far from that as it was possible to be. While the kids and Maria were at St Lucy’s, Manrique was setting to work on an elaborate plan to murder them all.

On 6 October he placed an order with gas company BOC for two canisters of carbon monoxide. Rather than have them delivered to his home — where his family might spot the delivery — he asked a colleague, Jairo Campos, if he could have them dropped off at his home in Parklea, a 45-minute drive away.

He told a curious Mr Campos he needed the gas to calibrate carbon monoxide levels in a covered car park and couldn’t store the tanks in the office. He paid his colleague around $400 for the bother.

But chemical experts at the inquest said the particularly pure form of carbon monoxide Manrique ordered was entirely unsuitable for testing background gas levels, which are often full of other substances.

GAS DELIVERIES ‘A BIT ODD’

On 7 October, Robert Lamont of logistics firm Linfox had the first canister of carbon monoxide on his truck.

Surprised to be delivering a gas with usually only niche industrial uses to a new customer at a residential address, he phoned the number on the docket. A man, presumably Manrique, answered and told him he was just storing them at the residential address and would shortly take them to a job on the Central Coast.

With no reason or company guidance not to, Mr Lamont completed the delivery.

On 10 October the second canister was delivered by Daniel Reilly, another Linfox driver. He told the inquest he also thought the delivery was a “bit odd”. In his 10 years of delivering gases and chemicals he had only delivered carbon monoxide around four times, and never to a home. He too called Manrique and was reassured.

On the 11 October, Manrique collected both tanks from the Mr Campos’s home.

“It is inescapable that the information relayed to BOC, Linfox and the Camposes was false,” Mr Casselden said.

In the meantime, Manrique had become an avid Bunnings shopper.

“Fernando went to Bunnings in Belrose on the 8th, 11th, 12th and 13th October to purchase materials to pump carbon monoxide into his house,” he said.

There were hoses and pipes, but one of those materials was just a simple padlock to lock the garden shed and hide the canisters.

Mr Casselden dismissed any suggestion Maria knew what her husband was up to.

“Why would he take these steps if Maria had evidence of Fernando’s evil plan?” he said.

“Police found the (gas) cylinders behind the house connected with hoses up to the roof where they were connected with metal clamps and then into the bedrooms.”

For at least five days they went about their lives as, just metres away, Manrique busily constructed the means for their death.

MUM ABOUT TO COME INTO MONEY

Maria was just as energetically planning for their future. She had completed a TAFE certificate 3 in education support opening up job opportunities as a teacher’s aide.

Doctors appointments were in the diary. She had just been approved for $25,000 worth of NDIS support for Elisa. She would never live to know it, but the NDIS had approved $25,000 for Tin as well.

“Her financial situation going forward would have been better off than it was for years,” said Mr Casselden.

“She was looking forward to life without Fernando and looking after the kids with assistance.”

Maria’s phone call home, at around 11am, was the last confirmed sign of life from the mum. At a similar time, Manrique was spotted in the garden.

At about 2.30am the next day a neighbour said they heard a dog barking from the direction of the house. It’s possible it was Tequila and may have been the final noise uttered from the home.

The inquest heard it was likely Manrique went to the shed and, as Maria, Elise and Tin slept, turned on the gas.

When carbon monoxide enters the body it attaches to haemoglobin, which delivers oxygen around the body, to form carboxyhaemoglobin which actively inhibits that process. Levels of 30 per cent or more of carboxyhaemoglobin in the body can be fatal. Toxicity levels in the Manrique-Lutz family were close to 70 per cent.

Questions remain around whether Manrique intended to flee, perhaps to the Philippines. But Jamie said he had never discussed moving to Manila. Besides, he knew how lethal the gas was so why return to the house? Every door in the home was locked.

On the Monday morning, Ms Brimble became concerned when Maria and the kids didn’t arrive at St Lucy’s. She phoned police and asked them to perform a welfare check at the Davidson home.

When officers arrived the home at 10.55am, everything appeared immaculate.

Ms Brimble insisted they look further — the cars shouldn’t be there at this time on a Monday and why wasn’t Tequila barking?

The Police forced entry and found Fernando unresponsive, face down in the hallway, “grey in colour and firm to the touch”.

Maria and Elisa were unresponsive in one bed, Tin in his. Tequila lay dead in Tin’s room.

Fans in each of the rooms were on full pelt — possibly to spread the gas all the more effectively.

“For reasons we may never know, Fernando carefully planned this tragedy, the silent deaths in the night of his wife, two children and himself,” said Douglas Spencer, representing the family of Manrique.

CAN ANOTHER TRAGEDY BE PREVENTED?

Since the Davidson deaths, BOC has tightened its rules around the purchase of carbon monoxide. Customers must be registered and approved by BOC, should be a business, and a declaration has to be completed to detail how the gas will be used.

But drivers have no access to this declaration and still have little guidance on dealing with deliveries of dangerous substances to homes.

“There is no legislation to stop carbon monoxide being delivered to residential addresses yet it has no known domestic use,” said Mr Casselden.

He asked the coroner to consider listing carbon monoxide over a certain purity level on the poisons standard, which would further beef-up restrictions.

But whether it would have prevented the Manrique-Lutz family deaths is debatable. Manrique ordered the carbon monoxide through his company and could easily have filled out the declaration with a plausible use. And deciding what constitutes a business, rather than residential address, is fraught with difficulty.

As the inquest came to an end Peta Rostirola spoke fondly of her friend.

“Maria faced the challenge of two young children with autism with fire, grace and an enduring sense of humour,” she said.

“She knew Elisa and Martin loved her and that made her love them harder. Life loving Elisa and Martin was all she needed”.

The coroner will hand down her findings on 17 May.

If you or someone you know is affected by family violence, call 1800 RESPECT on 1800 737 732 or visit www.1800RESPECT.org.au In an emergency, call triple-0

benedict.brook@news.com.au