The lawyer of an Argentine man who shot his parents dead has revealed how he 'violated' his stepfather's corpse, ate his flesh and committed an obscene act over his dead mother's body.

Leandro Acosta, 25, and his step-sister Karen Klein, 22, who have been lovers for six years, admitted to murdering their parents and burning their bodies as revenge for the 'years of sexual abuse' inflicted on them and their 11-year-old twin siblings.

Acosta's lawyer Monica Chirivin has told MailOnline the entire, gruesome story of the murder in Pilar, Buenos Aires, as told by the killer himself.

From inside a special psychiatric unit, Acosta confessed he had been planning the gruesome murders of his step-father Ricardo Klein, 54, and mother Miryam Kowalczuk, 52, for some time.

His mental state had been worn away by the years of abuse he suffered at the hands of Klein, who began raping him aged six, and Kowalczuk, who 'involved him in threesomes' as a boy.

No remorse: Leandro Acosta (right), 25, and his step-sister Karen Klein (left), 22, who are also lovers, killed their parents and burned their bodies

Gruesome discover: The murders were uncovered when police found part of the mother's pelvic bone and spine in a bucket, and 16 huge refuse bags 'containing human remains' in a nearby alley (pictured)

Acosta shot Klein in the head while he slept in his underwear, got 'sexually excited' and began violating his dead body.

At that very moment, his mother walked into the room and began screaming: 'What have you done, you son of a b***h!'

He turned the gun on her and shot her – again and again. He later cooked his father's flesh over a pyre and ate it.

He said: 'It [step-father's flesh] tasted like pork, a tad salty but delicious.'

Acosta felt no remorse for killing his mother, saying: 'She was a whore and a drunkard, I did justice my way.'

Chirivin said eating his step-father's flesh was 'almost a pleasure' for Acosta, who claimed he had been raped by several of his mother's lovers.

The murders were discovered when a relative could not get into the house and rang the police. They found part of Kowalczuk's pelvic bone and spine in a bucket, along with more human flesh 'readied for consumption', and 16 huge refuse bags - some of which contained 'human remains'.

Police Chief Dario Lutter said they also found three recently-bought axes, a machete, a shotgun and a 9mm pistol.

Klein's body was never found but forensic tests on the garbage bags, found in the house's yard, may reveal its whereabouts. Luminol tests have also been ordered to find traces of blood inside the house.

Justice or vengeance? Acosta (left) felt no remorse after killing his mother who he described as a 'whore and a drunkard', according to his lawyer Monica Chirivin (right)

Long-running feud: Horacio Klein (pictured), the brother of the slain father, said: 'My brother was a tough character but Leandro always answered back'

After murdering his parents, Acosta reported the couple as child molesters and requested a restraining order against them.

He then used the frame of a wheelbarrow to cart their bodies to a different section of the house where he kept them hidden for 11 days.

During this time, he beat the corpses, crushed the skulls, and impaled his mother's body on a spike and committed an indecent act over her corpse.

It [step-father's flesh] tasted like pork, a tad salty but delicious...She [his mother] was a whore and a drunkard, I did justice my way Leandro Acosta on his murdered parents

In her official statement, Acosta's step-sister and lover, Karen, claimed she only helped him 'clean up', but Chirivin believes she may have also helped drag the bodies and light the fire which they used to obliterate the body parts – and evidence.

She said Acosta, who is wheelchair-bound and fitted with a colostomy bag because of a long-running intestinal disorder, did not have the physical strength to light the pyre or lug the bodies around.

Neighbours are said to have recognised Klein - who moved in with the murdered couple after the death of her own mother - at the scene where the horrible-smelling bonfire was lit.

Once their parents had been murdered and their corpses set ablaze, Klein went off to her yoga class and Acosta went to work as usual.

Case prosecutor Eduardo Viaini has not allowed a psychiatrist to interview Acosta, who claims he is 'haunted by voices' and once turned to the infamous Umbanda cult, which is well known for its animal sacrifices.

Acosta's lawyer claims Viaini has limited the counsel's access to the case, delayed the handing over of paperwork and postponed his 'formal accusation' for another month because the case is 'too complex'.

Accomplice: Acosta's step-sister and lover, Karen (left), claimed she only helped him 'clean up' but Chirivin believes she may have also helped drag the bodies and light the fire which they used to burn the body parts

Acosta and Klein's 11-year-old siblings, who their deceased parents had together, are with social security because their father's brothers do not want to care for them.

Acosta seems to agree. 'Not the Kleins, not the Kleins,' he repeated over and over, fearing what might befall them.

Raúl Klein, the brother of the slain father, thinks Acosta had been planning this for years.

Another brother, Horacio, said: 'My brother was a tough character but Leandro always answered back. Money was always the issue.'

Meanwhile Roberto Klein said: 'There has always been resentment between him and his stepson and I believe this was a long time coming.'

The deceased Klein used to harass Acosta for not having a job and not bringing money into the home in spite of his manifest disabilities.

Police Chief Lutter said only female human remains had been found so far, adding: 'We received incoherent answers but heavily smoking fires had been raging for days. The main bedroom was empty and the mattress had been burned.'