Wellington, New Zealand — A New Zealand jury on Wednesday found a mother guilty of murdering her three young daughters after rejecting her defense that she was so mentally ill at the time she couldn't be held responsible.

Lauren Dickason, 42, had earlier admitted killing her 2-year-old twin daughters Maya and Karla and their 6-year-old sister Lianè at their home in the town of Timaru nearly two years ago.

She had pleaded not guilty to murder, arguing she was suffering severe depression that could be traced back to postpartum depression. Prosecutors acknowledged Dickason had suffered from depression but said it wasn't enough to warrant a medical defense. They said she killed her children out of anger and resentment.

They pointed to Dickason's troubling phone messages and online history in the weeks before the killings, including comments about wanting to kill her children and Google searches for "most effective overdose in kids."

Dickason and husband Graham Dickason, both qualified medical professionals, had moved from South Africa to New Zealand and settled in Timaru just days before the murders, seeking a more stable lifestyle away from the turmoil in their home country.

Lauren Dickason at first tried to kill her children using zip ties and then suffocated them with pillows. She then placed them in their beds under the covers and tried to kill herself.

Graham Dickason, an orthopedic surgeon, returned from a work dinner to find his children dead. He later told police he knew his wife was struggling with her mental health and with motherhood but had no idea she was capable of killing.

The guilty verdicts on three counts of murder came after a four-week trial. Jurors deliberated over three days and voted 11-1 for conviction, a split allowed under New Zealand laws. Dickason faces a sentence of life imprisonment.

Radio New Zealand reported that Dickason was motionless in the dock as the verdict was read out in the Christchurch High Court, and then cried quietly as she left. Jurors could also be heard crying, RNZ reported.

Dickason's parents issued a statement saying the deaths were the result of their daughter's debilitating mental illness.

"We would like to encourage families and individuals around the world to be aware of the symptoms of post-partum depression as early as possible, both for yourselves as well as close family and friends around you," Malcolm and Wendy Fawkes said in the statement, RNZ reported.

Detective Inspector Scott Anderson said police wanted to express their deepest sympathies to family members who would never get to see Liané, Maya and Karla grow up and live out their lives.

"Words cannot begin to express the tragic circumstances of this investigation," Anderson said in a statement.