Lawyers representing three sisters charged with murdering their abusive father have raised hopes of a non-custodial end to the trial.

New documents produced by state investigators seem to accept that the three teenage girls had been subjected to sexual, psychological and physical abuse by their father, Mikhail Khachaturyan.

Krestina, Angelina and Maria do not deny they killed their father in July 2018 as he was dozing in his armchair at the family home in northern Moscow.

Neither do they deny how they did it: dousing him with pepper spray, hitting him with a hammer and stabbing him 36 times to the neck, chest and heart.

But, they say, the episode came at the end of years of torture. They were the victims of an unhinged man with predilection for guns and violence.

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The case has proven extremely divisive in Russia, panning patriarchal values against the reality of unfettered domestic abuse. It comes two and half years after battery at home was controversially decriminalised.

In June, state investigators sided against the sisters, ignoring claims of self defence and charging them with premeditated murder. This crime carries a custodial sentence of between 8 and 20 years.

But the Khachaturyan sisters’ outraged defence team responded by pushing for an investigation into the father’s abuse.

Russian law does not ordinarily allow for a trial of the deceased (there are exceptions, when politically necessary, such as with the lawyer Sergei Magnitsky). But it does allow for the use of judicial mechanisms to establish facts about a case.

At the end of July, investigators concluded work on their probe. Their 22-page ruling, sent to all the parties, establishes at least seven cases of abuse against the sisters. The ruling may only be appealed by lawyers acting for the accused, and would involve a separate and messy trial.

According to lawyer Aleksei Parshin, who represents the middle daughter, Angelina, the ruling “proved” the girls’ argument of self defence.

It would be used to change the course of the trial in their favour, he told The Independent: “We trust that once the case is reviewed by prosecutors, they will look at the situation soberly. And that means that they would throw the case out.”

Another of the sisters’ lawyers suggested the system might not countenance such an obvious defeat. Reclassifying the crime was more possible – with correspondingly reduced sentences – once the Prosecutor’s Office came to review the investigators’ case.

“The review stage is usually automatic,” said Aleksei Lipster, lawyer for the eldest sister Krestina. “But the expectation is that the immense public interest will mean there will be more than a rubber stamp. Prosecutors will hopefully give the case the attention it requires.”

That prosecutorial review will be the subject of unprecedented scrutiny across Russia.

Over 300,000 people have already signed a petition campaigning for the sisters’ release. Many hundreds of thousands have engaged in a social media campaign, sharing photos under the hashtag #янехотелаумирать (I didn’t want to die).

That campaign has brought attention to the thousands of women convicted for assaulting or killing their abusive partners every year.

According to MediaZona, an investigative publication focussed on Russia’s judicial system, approximately 80 per cent of women held on murder charges are there after killing an abuser partner in self defence.

But from everyone in Russia is behind the sisters in their plight. The case has even split the family, with some relatives of the deceased father emphasising his religious identity over multiple reports of his more unsavoury character.

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A lawyer representing Mikhail’s relatives said that they would battle any attempt to reclassify the crime or drop the case. They would also appeal against the latest ruling, she added.

“The ruling only gives one side of a story and is marred with incompetence,” said Yuliya Nitchenko. “The only evidence that has ever been produced is the girls’ testimonies. There is no genetic evidence, no knickers, no audio recordings of the alleged abuse. This despite being given the latest iPhones.”

The girls, Ms Nitchenko claimed, were “cold blooded murderers” acting in full knowledge of what they were doing.