The Danish man sentenced to life in jail for the murder of journalist Kim Wall aboard his homemade submarine was arrested on Tuesday after a failed prison escape bid led to a standoff with police.
Using an object that "looked like a pistol", Peter Madsen threatened a prison employee to break out of the Herstedvester Prison, penitentiary director Hanne Hoegh Rasmussen told reporters.
Madsen then jumped into a white van and forced the person behind the wheel to drive several hundred metres (yards) before the vehicle was stopped by police.
Police said they were investigating the driver but did not for the moment consider him to be an accomplice.
Police were able to handcuff Madsen but because he was wearing what appeared to be a bomb belt, police backed away and a standoff ensued for several hours while police waited for explosive experts to arrive, Copenhagen Vestegns police inspector Mogens Lauridsen said.
"There is nothing at this point to indicate that (the belt) contained explosives ... We think it was fake," Lauridsen said, adding that an investigation was underway to be certain.
Police finally hauled Madsen away after more than two hours.
Rasmussen meanwhile refused to comment on media reports that the prison employee was a female psychologist and that Madsen had taken her hostage.
The Herstedvester Prison is a high security facility with space for 161 inmates in need of psychiatric or psychological care, and for sex offenders.
Inmates are not typically locked up all day, a prison spokeswoman told AFP, refusing however to comment on Madsen's particular case.
Prison officials were tightlipped about the details of how Madsen was able to break out.
"This is a closed prison. We are examining our security procedures to see if they have been respected and if they need to be reinforced," Rasmussen said.
Police inspector Lauridsen said Madsen had not yet been questioned.
"He will be soon though," he added.
Photos from the standoff scene showed Madsen sitting on the grass by a leafy wall next to a road a few hundred metres from the prison in a residential area, with police officers lying prone on the ground pointing their weapons at him.
- 'Pathological liar' -
Madsen, a 49-year-old submarine enthusiast, was convicted in April 2018 of murdering the 30-year-old award-wining journalist as she interviewed him on board his submarine in August 2017.
In a documentary that aired in September, he confessed for the first time to the killing, after having insisted during the trial that her death was an accident.
"There is only one who is guilty, and that is me," Madsen said in the documentary.
In a case that made headlines around the world, Madsen had however admitted to the court that he chopped up her corpse and threw her body parts into the sea.
Madsen changed his version of events several times after his arrest and throughout his trial, but ultimately testified that Wall died when the air pressure suddenly dropped and toxic fumes filled his vessel while he was up on deck.
In the documentary, Madsen said however he and Wall had a discussion that "shook things up", and that's what caused him to kill her.
An autopsy report presented at length during the trial concluded that Wall probably died from suffocation or having her throat slit, but the decomposed state of her body meant examiners could not determine the exact cause of death.
Fourteen stab wounds and piercings were however found in and around her genital area.
Madsen had told the court he stabbed her because he wanted to prevent gases from building up inside her torso that would prevent it from sinking to the seabed.
Psychiatric experts who evaluated Madsen for the court found him to be "a pathological liar" who poses "a danger to others" and who was likely to be a repeat offender.