The man accused of the axe-murder of Tara Costigan had allegedly pledged to kill the next woman to take out a domestic violence order against him, according to court documents.
Police have also alleged that Marcus Rappel, 40, fatally struck Ms Costigan while she carried their newborn baby in her arms.
Rappel appeared in a courtroom packed with Ms Costigan's family and friends on Tuesday, and was committed to stand trial on four charges relating to the domestic violence attack in late February.
New details about the alleged murder emerged from court documents tendered on Tuesday.
Ms Costigan turned to the court system for help just one day before her death, after giving birth to a baby girl and breaking up with Rappel, with whom she had been in a tumultuous and fractious relationship since late 2013.
She applied for and obtained an interim domestic violence order on February 27.
Court documents reveal that Rappel was served with the order - something often seen as a potential trigger of violence by domestic violence experts - the next day, before allegedly murdering Ms Costigan.
According to court documents, he allegedly told his new girlfriend:
"I did say if another girl slapped another DVO on me I will kill her."
A few hours later, Rappel is accused of driving to the Duggan Street home in Calwell where Ms Costigan was staying.
It is alleged he had an axe with him, and forced entry into the home, where Ms Costigan was feeding their seven-day old baby.
Ms Costigan, carrying her newborn, ran to the laundry, and her sister tried to pull her through to the garage.
Rappel allegedly struck her with the axe and she fell to the ground. At the same time as striking Ms Costigan, the axe allegedly connected with the hand of the sister, Rikki Schmidt, severing a tendon.
Ms Schmidt's partner Bryce Bullman then stepped in, knocking the axe out of Rappel's hands and struggling with him.
A neighbour came in and saw Rappel, taking him by the arm and leading him out of the unit.
Rappel, according to court documents, is alleged to have said:
"I killed her, I killed her, I think I killed her."
Ms Costigan's other two children, aged 11 and nine, were in the house at the time.
Police arrived and arrested Rappel, who is said to have told them:
"Can I say something? I murdered someone. You're going to use everything. I'm never getting out."
"Come on lads, what do you think I'm gonna do? Plead not guilty?"
Rappel is expected to appear in the ACT Supreme Court next week. He was committed from the ACT Magistrates Court by Magistrate Karen Fryar.
With Michael Inman