Greta's parents bought her and her fiancé a Christmas gift. They never imagined it would be fatal.

Greta Otteson and her fiancé, Arno Els, were recently engaged and in love. The pair had moved to Vietnam last year, taking out a lease to run the red-roofed Silverbell Villa, a nine-bedroom property in Hoi An.

They had their whole lives ahead of them.

But their great adventure was cut short when 33-year-old Greta, from Wales, and Arno, 36, from South Africa, were found dead on Boxing Day, just three weeks after their engagement.

The couple's bodies were found in separate rooms of the Hoi An Silverbell Villa. Their cause of death was soon confirmed to be from methanol poisoning.

Police believed the source was a "homemade" bottle of limoncello bought from a local restaurant on Christmas Eve, according to The Sunday Times.

Greta's parents, Paul and Susan Otteson, have since shared they were the ones who bought the couple the alcohol as a gift.

Despite eight months going by, Paul and Susan say they're still desperate for justice.

According to the BBC, the barman who allegedly made the limoncello was charged in February and is being held while investigations continue.

The family, however, says they've received no further updates from police since then.

"We can't move on," Paul said.

Watch: Warning to tourists as sixth traveller dies In Laos from methanol poisoning.

Before their deaths, Greta and Arno regularly posted happy snaps to social media while running the villa.

In April, Greta said she was "still pinching myself that I'm here."

Paul told The Times the couple were "so happy" together.

"We were so happy she picked Arno. He was such a lovely boy. Arno was a great musician, composer and lyricist," he said.

"They were a loving couple with their life ahead of them. The tributes we have had from around the world are unbelievable."

In November, Paul and Susan travelled to Vietnam to meet Arno for the first time. The BBC reports that during their stay, the family ate at a well-known Italian restaurant, Good Morning Vietnam, where they enjoyed the food and received free shots of homemade limoncello at the end.

Arno and Greta announced their engagement the following month, sharing a photo of them hugging at the beach.

When Paul and Susan were thinking of a Christmas present for the couple, they remembered the fun evenings spent at the restaurant and ordered some of its limoncello to be delivered to Greta's house.

On Christmas Eve, Greta and Arno enjoyed dinner at a local restaurant and came home around 10pm. Two limoncello bottles were delivered to their hotel reception.

The couple is believed to have drunk the alcohol and gone to bed.

When they woke on Christmas Day, Greta messaged her parents complaining of "the worst hangover ever" and said she was seeing "black spots" in her vision, per The Times.

Thinking it was just alcohol-related, the couple decided to try to sleep it off, unaware they needed medical assistance. Staff found their bodies on Boxing Day morning.

The deaths came just weeks after six people, including Melbourne teens and best friends Bianca Jones and Holly Bowles, died from drinking contaminated alcohol in Laos.

Greta and Arno in their engagement announcement. Image: Facebook/Greta Otteson.

In February, the BBC reported police arrested a barman who worked at a restaurant in Ho An for "violating regulations on food safety" by "using used 70-degree medical grade alcohol, along with filtered water, lemon peel and white sugar to create two bottles of limoncello" — an offence that could carry a maximum prison term of seven to 15 years.

Paul and Susan were warned investigations would take time in Vietnam. A suspect could be held for a year before being charged or released.

But they need answers.

"We just want justice," Paul told the publication.

"We can't move on. Susan's asking me every morning when we wake up, 'is there any news? Is there any news?' I have to say 'no, nothing yet'.

"It's about accountability."

The restaurant that is believed to have delivered the limoncello is reportedly still open. Paul and Susan say they have yet to receive an apology.

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What is methanol poisoning? And what does it do to you?

Methanol is extremely poisonous. Sometimes even as little as a shot can be fatal.

The alcohol is odourless, colourless and flammable, similar to ethanol, only it's not safe for drinking.

Dr Brad McKay told Mamamia's twice-daily news podcast, The Quicky that methanol poisoning initially presents as similar to a hangover, making it difficult to pick up on.

"Often, if you've had a night out drinking, your body ends up metabolising all the alcohol first. Your liver takes on ethanol in preference… once that has been used up then your body starts to move on to metabolising methanol," he said.

This could be several hours after drinking, so the following day you could feel a lot worse.

Methanol is toxic because of how our body metabolises it.

While ethanol is metabolised into a toxic compound called acetaldehyde, it rapidly converts to acetate (which is found in common vinegar and is something the body can use for several purposes).

However, methanol breaks down into other compounds that are far more hazardous.

Methanol is metabolised into formaldehyde (a chemical used for embalming corpses) and formic acid (the chemical that gives ant bites their sting), Dr McKay said.

"You do only need that small amount to cause a problem. It's highly poisonous," he said.

Methanol poisoning can cause nausea, vomiting and abdominal pain. Blindness is common and often permanent too, as is organ damage.

Symptoms of methanol poisoning.

In its early stages, methanol poisoning may just seem like you're drunk. Pay attention if your intoxication levels feel disproportionate to how much alcohol you have consumed.

Severe symptoms do not usually occur until 12 to 24 hours after consumption.

Methanol poisoning symptoms can include:

• abdominal pain

• nausea

• vomiting

• breathing difficulty

• vision problems (blindness, dilated pupils, flashes of light, tunnel vision, changes in colour perception, blurred vision)

• seizures

• and/or comas

Smartraveller urges Australians to be alert to drink origins and spiking, particularly with spirit-based drinks, including cocktails.

Contaminated drinks could include local home-brewed spirits, spirit-based drinks and brand-name alcohol, as labels on bottles aren't always accurate.

To protect yourself from drink poisoning, Smartraveller says:

• consider the risks when drinking alcoholic beverages

• be careful drinking cocktails and drinks made with spirits

• drink only at reputable licensed premises

• and avoid homemade alcoholic drinks.

Feature image: Facebook/Greta Otteson.