The woman is also suspected of attempted murder against her mother at the same as killing her father last year and has also been connected with the drowning of her husband in 2015.
The woman has been dubbed the 'Arboga woman' after the scene where the alleged violent crimes took place, a summer cottage in Arboga, central Sweden.
The 42-year-old woman, who ran her own business and has six children, is trained as a social worker and has no previous convictions.
Also involved is her boyfriend, a man from Afghanistan who came to Sweden as a lone refugee from Iran in the autumn of 2015, although his lawyer confirmed a day before the charges were pressed that the pair have broken up.
“There is not just a chain of indices. The so-called boyfriend is cooperating, and there are also witness testimonies that are important in this context. It is my assessment that she will be can for the crimes against her mother and father, not for murder but for intent,” criminologist Jerzy Sarnecki told news agency TT.
The woman, who has been charged with the murder and attempted murder of her parents, as well as the murder of her husband, denies all charges.
Her former boyfriend has pleaded guilty to the crimes against the parents and said that it was the woman that drove him to the summer cottage where the deeds took place and gave him the knife that was used as the murder weapon, reports TT.
Technical evidence, including blood from the father found on the passenger seat of the car used on the night of the murder, has been found against the boyfriend.
DNA from the boyfriend was also found on the father as well as footsteps matching his shoes in the house.
An image from the police investigation showing a blood trail in the summer cottage. Photo: TT
But there is no physical evidence connecting the crime to woman, who is instead charged on other evidence including notes she wrote while in custody that revealed detailed knowledge of the events.
Prosecutor Jessica Wenna previously claimed that the woman “instructed and directed” the boyfriend.
The 42-year-old also has no alibi for the night of the murder and has given up to nine different versions of what she did at the time of the crimes.
This will affect her trustworthiness – a key issue for the jury during the trial, said Kerstin Koorti, an experienced criminal lawyer, to TT.
The woman's defence maintains that the boyfriend committed the deed on his own.
Evidence for the alleged murder of the woman's former husband is more fragile, according to Sarnecki and Koorti.
The former husband was found drowned near the same cottage a year before the crimes against the parents in August 2016.
Prosecutors consider the husband's death have been proved not to be accidental, based in part on new analysis from the opening of the drowned man's grave in November 2016, when forensic examination showed that he is unlikely to have drowned in the Hjälmaren lake near the summer cottage, reports TT.
The woman, who made a claim against the husband's life insurance a few days after his death, is said to have attempted to persuade others to kill him.
Sarneck said that this was “incriminating, but the question is whether it is enough.”
As investigations immediately after the man's death did not determine the cause, it would be very difficult to convict for murder, he added.
Meanwhile, prosecutors representing the 42-year-old woman's mother and sister said that they would be “relieved” once the trial was over.
“Over the years, the family has supported and helped the woman in every way possible. They have bought apartments, cars and given them large sums of money. This is a tragedy,” prosecuting lawyer Susanna Cleve said, reports TT.
Cleve chose not to say anything about her client's memories of the night of the father's murder, in which the mother sustained serious injuries.
“Since August last year their lives have been completely ravaged. They have been through an indescribable trauma and now find themselves in the deepest and most difficult sorrow,” Cleve said.
The husband to the 42-year-old was “afraid” of her in the time preceding his death, said prosecution lawyer Brage Åman.
“The relatives immediately suspected that it was not an accident that was behind the husband's death in 2015. This was based on what the man told them about his marriage to the 42-year-old woman,” said Åman.
“Shortly after they began their relationship he began to speak about circumstances that made him feel quite bad. He was even afraid of his wife,” the prosecutor added.