Danish inventor Peter Madsen, accused of murdering Swedish journalist Kim Wall on board his homemade submarine, insisted her death was accidental while prosecutors argued his fascination for beheadings and impalings suggested otherwise.
Madsen has claimed that Wall, a 30-year-old freelancer, died when the air pressure suddenly dropped and toxic fumes filled his vessel on the night of August 10, 2017, while he was up on deck.
He has admitted dismembering her body and throwing it overboard, but denies the charges of premeditated murder and sexual assault.
Wall had gone out for a sail with Madsen to interview him for a profile she was writing of the eccentric inventor, well-known in Denmark.
The prosecution has painted a picture of Madsen as a sadist who murdered Wall as part of a sexual fantasy, though neither Madsen's own explanations nor an autopsy have provided any clarity on the cause of death, nor a motive.
Wall's dismembered body parts, weighed down in plastic bags with metal objects, were recovered from waters off Copenhagen in the weeks following her disappearance.
He has changed his account of what happened several times.
Prosecutors on Wednesday showed the court three videos found on Madsen's hard drive. On one, a real woman had her throat slit; another was an animated film of a woman having her throat slit and being decapitated; a third was animated film depicting a woman having her throat slit before being decapitated and impaled.
Texts on women being impaled were also found.
Madsen, who told the court he occasionally filmed his sexual encounters with women with an action camera mounted on his forehead, refused to watch the films, calling them "revolting".
He argued that other people also had access to the hard drive, including a woman identified as "A", a photographer he claimed was into violent sex videos.
Often argumentative and irritated during questioning by prosecutor Jakob Buch-Jepsen, Madsen rejected any link between watching such videos and actually beheading someone.
Asked by the prosecution if it was a coincidence he was now on trial, Madsen retorted angrily: "Jakob, would you think it was strange if you had seen a film about a nuclear bomb and then a nuclear bomb exploded?"
Madsen, 47, reiterated his argument that he searched for such material for "emotional reasons, not erotic reasons".
"That it happens just before I sail off with Kim Wall is conspicuous, but random. She died from lack of oxygen," Madsen insisted.
Thirty-seven experts and witnesses are expected to testify over the coming days to evaluate the credibility of Madsen's accident scenario, and help understand the psychology of the self-taught engineer, described by the prosecution as "a perverted polymorph, and highly sexually deviant".
According to the prosecution, evidence showed Madsen bound Wall around the head, arms and legs before beating her and stabbing her repeatedly in her genital area.
They say he killed her -- either by strangling or slitting her throat -- and cut her up with a saw, stuffing her torso, head, arms and legs in separate bags weighed down with metal objects, and dumping them in Koge Bay off Copenhagen.
On Wednesday, Madsen told the court the 14 stab wounds to Wall's genital area were intended to make her body sink to the seabed.
"I considered where gases build up inside dead people when they decompose. They do so in different places. Therefore I tried to puncture that region," he said.
"There is nothing sexual in the stabs hitting her vagina."
The prosecution said an autopsy showed the stab wounds were inflicted around the time of death -- either just before, at the time of or just after Wall's death.
But Madsen claimed they were inflicted "hours after" her death.
Asked about a text message he sent a woman friend on August 4 which read "I'm going to tie you up and impale you with a skewer", Madsden claimed it was just sexual role play.
He explained on the first day of his trial, on March 8, that he chopped up her body because he panicked and wanted her dead body off the submarine but couldn't lift her out in one piece.
"I don't see how that mattered at that time, as she was dead," he said with a grin.
Wall, who criss-crossed the world in search of unique and quirky stories, was reported missing by her boyfriend after she failed to return home from her interview with Madsen on board the 60-foot (18-metre) vessel.
The prosecution has said it will seek a life sentence, which in Denmark averages around 16 years, or safe custody, a legal alternative which would keep him behind bars indefinitely as long as he is deemed dangerous.
A verdict is expected on April 25.