Luay Sako, 39, kept his head down and at times punched himself in the face as Celeste Manno's mother read a statement to the Victorian Supreme Court on Monday.
Aggie Di Mauro had been sleeping in another room when Sako broke into their Melbourne home in the early hours of November 16, 2020.
Celeste Manno was killed by Luay Sako hours after she posted a photo of her boyfriend on Instagram. (James Ross/AAP PHOTOS)
She woke to the sound of Sako leaving the property and ran to the bedroom to find her daughter's lifeless body.
"I desperately tried bringing my baby back," she told the court through tears.
"I slept through the last two minutes and 39 seconds of my daughter's life. I was too late to protect her."
Sako began stalking and harassing Ms Manno about 18 months before he murdered her.
The pair had briefly been co-workers but he developed an infatuation with her because she was kind to him after he was sacked.
He started bombarding her with Instagram messages, professing his love and ignoring her requests to stop.
Luay Sako told a woman he would never hurt a soul, but later murdered her. (Con Chronis/AAP PHOTOS)
Over a 12-month period, he sent more than 140 messages to Ms Manno from a number of different Instagram accounts, with the communication becoming increasingly vulgar and degrading.
She went to police and obtained an intervention order against Sako but it didn't stop him contacting her.
He told Ms Manno he would never hurt a soul and queried why she would see him as a threat.
But he killed her on November 16, 2020, just hours after she posted a photo of her boyfriend for the first time on Instagram.
Sako drove to her Mernda home in Melbourne's northeast, scaled a fence to get into her backyard and then smashed her bedroom window with a hammer.
He broke into the room where Ms Manno was sleeping and stabbed her 23 times with a kitchen knife before going back to his car and driving to the police station.
Aggie Di Mauro has shared her grief about her daughter's murder. (Con Chronis/AAP PHOTOS)
Ms Di Mauro said she blamed the police's lack of action and herself for her daughter's murder.
"The only other person I hate more than you (Sako) is me," she told the court.
"He not only murdered my sweetie but he did it under my watch.
"He destroyed my self-worth and any notion of being a good mum ... he's left me with a lifetime of self-loathing, guilt and remorse."
Sako kept his head down during her statement but Ms Di Mauro yelled at him to look at her, calling him a gutless wonder, a coward and a beast.
Ms Manno's father Tom and brother Alessandro also confronted Sako, saying he had ruined every joyful occasion because Celeste was no longer there.
Celeste Manno's brother Alessandro and father Tom confronted killer Luay Sako in court. (Con Chronis/AAP PHOTOS)
"It has been a hell of a nightmare and it felt like it was never going to end," Alessandro said.
Sako pleaded guilty to Ms Manno's murder on Monday but he argued he only stabbed her twice rather than 23 times.
The 39-year-old, who is representing himself, claimed some of the wounds were caused by glass from the smashed window.
Forensic pathologist Paul Bedford told the court the majority of Ms Manno's injuries would have been caused by a knife and there was no glass found in her wounds.
The plea hearing continues on Tuesday.
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