Coroner Joe McCrisken described the deaths of Giselle Marimon-Herrera, 37, from Colombia, and her 15-year-old daughter Allison as "barbaric", and "one of the most difficult" inquests he has ever presided over.
The bodies of the mother and daughter were discovered in an apartment in Newry, Co Armagh, on March 7 2019 along with Russell Steele, from Kilmarnock, by police after they had all been reported missing.
Mr McCrisken found Ms Marimon-Herrera died from asphyxiation and suffocation and Miss Marimon-Herrera died due to manual strangulation and suffocation. Their chihuahua dog was also found dead.
He said he could not be satisfied that Ms Marimon-Herrera had been sexually assaulted, but that there is evidence her daughter had been raped.
Steele was found to have died by hanging and had intended to die.
The inquest heard Steele's family had been kept informed of the proceedings but chose not to attend.
Mr McCrisken thanked members of the Marimon-Herrera family who attended the inquests at Armagh court house for their "dignity" throughout the police investigation and inquests, telling them they have been "through hell over the past year".
He also thanked the Police Service of Northern Ireland for a "genuinely excellent" investigation.
At the opening of proceedings on Thursday morning, Mr McCrisken said he was holding separate inquests into the deaths of Ms Marimon-Herrera and her daughter, and Steele.
He heard evidence about events in the run up to the deaths.
A statement from Ms Marimon-Herrera's sister Paola was read to the inquest.
She described how her sister had arrived in Northern Ireland in 2016 after separating from her Portuguese husband, and was followed by her daughter in 2017.
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She also told the inquest that her sister had felt Steele was "controlling" and she had wanted to end the relationship.
PSNI Investigating Officer Victoria Holmes said text messages exchanged between Steele and Ms Marimon-Herrera revealed a recent argument which included an attempt by her to end the relationship.
Statements from two Polish men, Szymon Kosecki and Pawel Bronk, who had been work colleagues of Steele, were read to court.
They are believed to be the last to have seen Ms Marimon-Herrera and her daughter alive after meeting up with the mother and Steele for a night out on Saturday March 2 at Brass Monkeys in Newry.
They returned to the Glin Ree Court apartment where they saw Miss Marimon-Herrera with her pet dog.
They stayed for around an hour for drinks, leaving at around 3am.
Ward Devlin, an ex-partner of Ms Marimon-Herrera, gave evidence to the inquest about how he raised the alarm after she failed to respond to messages for several days.
Neighbour Gerard Doran is believed to be the last person to have seen Steele alive.
He recalled to the inquest seeing Steele standing at the front door of the apartment complex on Sunday March 3 holding a holdall and a plastic bag, looking "agitated" and "unable to stand still".
"I thought his behaviour was very strange at the time," he told the inquest.
An examination of a laptop found in the apartment revealed research on lethal doses of paracetamol at 5.20am on Monday March 4.
Mr McCrisken put it to Ms Holmes that Steele had been preparing to leave before changing his mind and returning to the apartment where he took his own life.
"If you are asking my personal opinion then yes," she responded.
Steele had had two passports, his phone and a pair of torn ladies underwear which DNA evidence found were likely to have belonged to Miss Marimon-Herrera in his pockets.
The inquest also heard that phones likely to have been used by Ms Marimon-Herrera and her daughter had no recoverable information on them.
"It appears that the information was deleted from both devices," Ms Holmes said.
A statement from Steele's ex-wife was read to the inquest.
Margaret Steele said she met him through church as he battled a heroin addiction.
They had a temporary split in 2010 when he relapsed but in total they were married for 17 years and had two children together.
The marriage ended after she discovered her husband was having an affair with Ms Marimon-Herrera who he had previously met in Spain before reconnecting via social media. He then left their home in Kilmarnock to move to Northern Ireland.
The inquest heard Steele had a criminal record, which included a conviction for an assault which led to an eight-month prison sentence.
Miss Marimon-Herrera was described as quiet, and having battled with an eating disorder in the past, but had been doing well at the time of her death. She was a pupil at Newry High School.
Delivering his findings, Mr McCrisken said neither Ms Marimon-Herrera nor her daughter would have been likely to have been able to fend off Steele.
"The killing of Giselle Marimon-Herrera and her 15-year-old daughter Allison by Russell Steele was barbaric," he said.
"Giselle Marimon-Herrera was a woman of small stature. Her 15-year-old daughter and her would have been unable to offer any resistance against an attack by Russell Steele.
"I am satisfied that he acted alone for a reason that is unknown. The killings were an impulsive act carried out by an individual with a history of aggression and violence."