Bartender Cian Sweeney served a tourist a drink with a smile. But she knew who he really was.

Content warning: This post includes descriptions of domestic violence.

There are plenty of European expats who end up working in Mallorca for a taste of island life.

Sun, sand, heat and Spanish culture is hard to resist.

But when an Irish tourist walked into a Mallorca bar and struck up a conversation with the barman, it wasn't what it seemed.

He introduced himself as Cian Sweeney, but she knew she'd seen him before.

She knew he wasn't what he said he was.

* * *

To most of their family and friends, Colin Whelan and Mary Gough looked to be in a loving relationship.

They'd met in a pub in Ireland in the early '90s and friends say from day one, Mary was "madly in love".

Soon they were engaged and in the docuseries Getting Away With Murder: The Killing of Mary Gough, one of her brothers recounts walking her down the aisle on her wedding day.

"Mary looked beautiful on the day. But she was nervous. There were mixed emotions," he recalls.

It's obvious from footage taken at the wedding, which features in the documentary, that Mary felt uncomfortable, barely even smiling.

Mary's mum Marie had also noticed something wasn't quite right.

"She didn't seem happy. That's the way I felt about it. She wasn't as happy as I thought she'd look," Marie said.

Watch the trailer for True Crime Conversations. Post continues below.

The honeymoon also did little to lift Mary's spirits.

"After Mary came back from the honeymoon, I noticed a change. Mary was quieter and she wasn't dressed up as she used to and Colin didn't seem the same," Marie told The Irish Mirror.

Then on March 1, 2001, 29-year-old Whelan called emergency services.

He claimed that Mary, who was just 27, had fallen down the stairs accidentally, while wrapped in a duvet. Whelan said that at the time of the incident he was in the shower and heard the "thud, thud, thud down the stairs".

While he waited for the ambulance, the call operator instructed Whelan to perform CPR, but it was too late.

Mary was dead by the time paramedics arrived.

Immediately, those who attended the scene noticed something wasn't right.

Whelan had scratches on his chest, which he claimed were caused as Mary "grasped out and grabbed" at him for help as she lay at the bottom of the stairs.

There were also no signs on Mary's body that Whelan had performed CPR as instructed by the emergency services call operator.

Then a post-mortem examination revealed the truth. Mary's injuries were not consistent with a fall down the stairs. She'd been strangled.

Mary Gough and Colin Whelan. Image: BINGE.

Police turned their attention immediately to Colin Whelan, seizing his phone and computer.

It was his Google search history that undid him. In the run up to the wedding, Whelan had looked up "how to get away with murder" and made other searches on how to asphyxiate someone.

He had also looked up American serial killer Henry Louis Wallace, who was known to have strangled his victims without leaving a mark.

Wallace did this by placing a towel underneath the ligature, which acted as a buffer.

A towel had been found close to Mary's body.

Marie still vividly remembers the moment she was informed her daughter's death wasn't accidental, but a murder.

"It was just shocking. I started shaking from head to toe. Everybody was very emotional," she told the docuseries.

"The week leading up to what happened to her, she'd ring me every evening. When I think about it now, I realise she must have been trying to tell me something but couldn't say it."

Investigators then found a motive for Whelan's actions, discovering that he had increased their life insurance policy so that he would receive approximately $750,000 in the event of her death.

He had also been cheating on Gough — embarking on a relationship with a woman in Wales over the Internet. The pair had been sending love letters to one another, but had never met in person.

Whelan was arrested and charged with Mary's murder.

But while on bail awaiting trial, Whelan disappeared. At first police thought he'd taken his own life after his car was discovered at the edge of nearby cliffs, an empty bottle of gin on the driver's seat.

Three years passed.

Then an Irish tourist who was on holiday in Mallorca walked into a bar and immediately recognised the man who served her drink: it was Colin Whelan.

He told her his name was Cian Sweeney, but she was convinced otherwise, having read about Mary's murder and Whelan's disappearance in the newspaper.

She was right. Whelan had travelled to Mallorca using a fake passport and nobody had ever worked out who he was - until now.

The tourist reported the sighting to the Spanish police, and Whelan was arrested at the bar.

He was extradited back to Ireland in 2004 — three years after his wife's death.

Once back in Ireland, Whelan pled guilty to the murder. He was sentenced to life in prison, with a possibility of parole.

Marie with her daughter Mary Gough. Image: BINGE.

Reflecting on the case, former Detective Inspector Pat Marry told Sky documentary Ireland's Most Evil Killers: "Colin Whelan was psychopathic, he was calculating, devious, and evil."

Looking back, Marie thinks Whelan never loved her daughter.

"He must have never thought anything of Mary and our family. He must have never loved her whatsoever and he had no thought for anyone but himself," she told The Irish Mirror.

Whelan has now been behind bars for 20 years, but could become eligible for parole in the next five. At this stage he has not been approved for early release.

Marie mourns her daughter's death every day.

"It's a curse I am carrying for life. He fooled everybody. We thought we knew him, but it was all an act."

If this has raised any issues for you, or if you just feel like you need to speak to someone, please call 1800 RESPECT (1800 737 732) – the national sexual assault, domestic and family violence counselling service.

Mamamia is a charity partner of RizeUp Australia, a national organisation that helps women, children and families move on after the devastation of domestic and family violence. Their mission is to deliver life-changing and practical support to these families when they need it most. If you would like to support their mission you can donate here.

Feature Image: BINGE.