Denmark's most notorious inmate, serving a life sentence for murdering a journalist aboard his homemade submarine, has sued the Danish state over legislation that bars him from cultivating new relationships, with the verdict due today.

A law introduced in 2022 restricts life prisoners to having visits, letter and telephone contact only with people already close to them before their conviction, during the first ten years of their sentence.

Peter Madsen, 52, claims the law violates his fundamental rights - to a private life - as defined by the European Convention on Human Rights.

The submarine enthusiast and self-taught engineer was convicted in April 2018 of the premeditated murder and sexual assault of 30-year-old award-winning Swedish journalist Kim Wall when she went to interview him on board his submarine in August 2017.

He confessed to chopping up her body and stuffing her head, arms and legs into plastic bags, weighing them down with metal pipes before tossing them into the sea.

His high-profile trial unveiled his interest in violent sex and snuff films of women being beheaded, skinned, tortured and impaled.

The gruesome crime gripped Denmark, one of the safest countries on the planet, and made headlines around the world.

A silent auction with Kim Wall's photographs on display at a ceremony for The Kim Wall
Memorial Fund at Superfine in March 2018 in New York City

Several years later, Danes were outraged when media revealed that a young woman claimed to have fallen in love with Madsen after starting a correspondence with him when he was in pre-trial detention and she was a minor.

That prompted the government to introduce the only legislation of its kind in Europe.

"When it was presented in parliament, (the debate) was directly targeting him," Madsen's lawyer Tobias Stadardfeld Jensen told AFP, although he noted that the legislation applies to all life prisoners.

'Invasive' legislation

Criminology professor Linda Kjaer Minke of the University of Southern Denmark said she believed Madsen's case was built on solid legal grounds.

"The law can be a violation of Article Eight of the European human rights convention. This article states that everyone has a right to respect for his private and family life and his correspondence," she said.

"The law shouldn't restrain the right of prisoners in general to protect a very (small) number of women who might need help and support."

She said it was a "shame" Madsen was the first convict to challenge the law in court.

"In the public debate, his crime overshadows the fact of how invasive this legislation is and that the Danish state may have gone too far."

Madsen was arrested after a failed prison escape bid led to a standoff with police in 2020

Madsen's lawyer Stadardfeld Jensen said the verdict would determine "whether we as a society uphold the principles that are described in international conventions or whether we fall back to satisfy public opinion, which (believes) Peter Madsen should be punished more harshly than anybody else."

Madsen has been divorced twice, marrying a second time while in prison in 2019. That marriage ended in divorce in 2022.

'Dating not a human right'

Stadardfeld Jensen insists Madsen has had almost no contact with the outside world since the law came into force.

In June, he was found guilty of smuggling out four letters to two women.

Stadardfeld Jensen said it was a "coincidence that those who wanted contact with him were women," and that most of the exchanges were about rockets, Madsen's true passion.

Four women who developed relationships with Madsen after he began serving his sentence attended the court proceedings in November.

Only one of them has had contacts of a romantic nature with Madsen, his lawyer said.

"There is a young woman who has developed feelings for him."

The Danish government is adamant that the law is needed to protect people from dangerous criminals.

"It is not a human right to make new friends or have dates when you're in prison for violent and bestial crimes," Justice Minister Peter Hummelgaard told AFP.

"The aim of the law is, among other things, to put an end to a repeat of previous examples where inmates contact young people and lure them into their web in a bid to win their sympathy or attention," he said.

Madsen's lawyer insists that is not the case for his client.

"He's a guy who knows that what he has done is very brutal and he has no sympathy for himself at all," said Stadardfeld Jensen.