German prosecutors have agreed to launch a criminal investigation into the disappearance of Briton Louise Kerton.

The then 24-year-old nurse vanished in the German city of Aachen last July.

Her father Phil believes she was murdered.

Senior officers from Kent Police returned from Germany on Thursday with news of the latest development.

Ms Kerton never arrived at Ostend

It was welcomed by her parents, who said it was long overdue.

Exam failure

The Kent nurse was on her way back to the UK after a visit to her boyfriend's family.

Her disappearance came days after she learnt she had failed her final nursing exams.

A spokesman for Kent Police said: "The public prosecutor has now agreed to record Louise's disappearance as a criminal investigation.

"This is a significant shift from the initial classification of that of a missing person inquiry.

All we want now is to find out what happened and get closure

Phil Kerton

"The objective has always been to convince the public prosecutor that Louise's disappearance was more than a simple missing persons inquiry and this has now been realised."

Mr Kerton, 57, said it should have happened six months ago.

"It was only in October last year that we realised that we weren't making any headway with the German authorities and since then it has cost all this pain and agony along with �30,000 to get things moving.

Life savings

"All we want now is to find out what happened and get closure.

"It has been totally frustrating but now the case is in the hands of people who have the power and resources to fully investigate the matter."

Ms Kerton, who lived with Peter Simon, 39, in Broadstairs, Kent, had visited his mother, Ramana, in Germany in July.

The last official sighting of her was when Mrs Simon took her to Aachen railway station.

Lucie Blackman was a friend of Louise

Mr Kerton hired formal royal protection chief Dai Davies to investigate his daughter's disappearance and criticised the German investigation.

He and his wife Kathy who are Welsh now live in Kent.

The couple have spent their life savings looking for their daughter and relatives from all over Wales have joined searches in Belgium and Germany.

Human rights

Earlier this year, a team of detectives from Kent travelled to Germany to try to persuade the authorities to start a fresh search.

Mr Kerton said the Germans regarded searching for missing people as an infringement of their human rights unless they were ill or depressed when they disappeared.

Ms Kerton's disappearance followed the high profile case of Lucie Blackman, the former air hostess found raped and murdered in Japan.

The two were friends and had attended the same private school in the south of England.