The sister of a British backpacker murdered in Thailand died in a “double tragedy” while nine weeks pregnant, an inquest has heard.

“No one knows” what caused the death of Laura Daniels, 30, despite extensive investigations, her family was told on Wednesday.

She died at Southampton General Hospital on September 16 2019 – five years after her sister Hannah Witheridge was found dead on a beach in Thailand.

A post-mortem examination was unable to ascertain a cause of death for Mrs Daniels, a paediatric nurse who lived in Great Yarmouth, Norfolk.

Her death while pregnant was a “double tragedy”, area coroner Rosamund Rhodes-Kemp said as she recorded an open conclusion.

Speaking at the inquest in Winchester, she said: “Given the post-mortem findings it is very difficult indeed to come to any conclusion other than open and that is because no one knows quite why Laura died when she did.

“No one knows, and that must be one of the hardest things for families and friends – for a young person to die and for despite all the investigation, all the inquest process we end up simply not knowing.”

The inquest, which began last month and finished on Wednesday, heard that Mrs Daniels had a complex medical history and had undergone numerous surgeries and treatments at various hospitals over the years.

On September 16 2019 she was found unresponsive in hospital shortly after speaking to staff and was pronounced dead.

In a heartfelt statement read out by the coroner, her husband Lewis Daniels said: “Laura was an incredible young lady who had so much desire to continue making the most of her life whilst having to deal with adversity very few people across the world will ever have to experience.”

He described the impact the tragic murder of Miss Witheridge had on the family, and how Mrs Daniels “spearheaded the fight for justice for her sister”.

He added: “Life was never going to be easy or the same again, we shared difficult times but we found happiness together.”

Mrs Daniels went on to qualify as a paediatric nurse and the pair were married in 2018.

The bodies of Miss Witheridge and 24-year-old David Miller, from Jersey, were found on the resort island of Koh Tao in 2014.

They had arrived in Thailand separately and met at the hotel where they were staying.

Two Burmese migrants who were convicted over the killings had their death sentences reduced to life imprisonment in 2020.

Wai Phyo and Zaw Lin had denied killing Mr Miller and raping and killing Miss Witheridge.

Lawyers for the two men had claimed evidence used in the case against them was mishandled and they made confessions under duress that they later retracted, raising questions about police competence and the judicial system in Thailand.

Human Rights Watch at the time called the verdict “profoundly disturbing”, citing the defendants’ accusations of police torture that were never investigated and questionable DNA evidence linking them to the crime.

But Thailand’s Supreme Court upheld the convictions.