With those words, a horrified mother began on Friday to explain the terrifying ordeal John Michael Gray, 27, put her family through in broad daylight in Civic on August 15 last year.

She and her three children had just left a shop near the Canberra Centre when Gray suddenly snatched her five-year-old girl and took off with the child under one arm.

The woman screamed for help, prompting a man described by Justice Michael Elkaim as "an unquestionably brave person" to chase Gray into a nearby laneway.

As Gray dropped the girl onto the ground, a knife fell out of his pocket.

Declan Smith, the man pursuing Gray, eventually caught up with the offender near a restaurant and performed a citizen's arrest before detaining him until police arrived.

In a victim impact statement read to the ACT Supreme Court at Gray's sentencing on Friday afternoon, the girl's mother described being unable to stop thinking about "all of the what-ifs".

"I keep replaying in my head the image of her little feet protruding under this man's arm as I ran after him," she wrote in the statement, which prosecutor Christina Muthurajah read.

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The woman said she and her daughter were both trembling in shock following the incident, while her other young children who witnessed it were also terrified.

"The only comfort they have is that the 'bad man' has been taken away," she wrote.

The woman also detailed how her usually confident daughter now often clutched her arm at shopping malls, feared some unfamiliar men, and experienced nightmares.

She expressed her gratitude for the bravery of those who had helped apprehend Gray and contact the police, as well as the officers who worked on the case.

Gray, who was on parole at the time of the offending, pleaded guilty last year to charges of unlawfully taking a child and possessing a knife in public without a reasonable excuse.

He has been in custody ever since the day in question.

His lawyer, Jonathan Cooper, on Friday told the court Gray was "coming up close to having done enough time" behind bars.

He submitted that Gray was now properly medicated for various mental health issues for the first time in his life.

The court also heard Gray was homeless at the time of the offending, using drugs and hearing voices telling him to "take a kid".

Gray wrote a letter himself, apologising and saying he felt like an idiot for what he had done while "delusional and sick".

In sentencing, Justice Elkaim said a pre-sentence report described Gray as having discussed a desire to commence a sexual relationship with the victim, which was "both ridiculous and deviant".

But the judge ultimately accepted that "the motive disclosed in the pre-sentence report did not cause the offending".

Rather, he found that "the offender's actions were the product of a psychotic episode".

Justice Elkaim said Gray clearly had serious mental health issues, but he could not forget the seriousness of the man's crimes and "the horrific experience endured by the young girl and her mother".

He sentenced Gray to two-and-a-half years in jail, with the term backdated to start in August 2020.

The judge imposed a non-parole period of 15 months, making Gray eligible for release this November.

He recommended, however, that the parole authorities refrain from letting the 27-year-old out of jail until an appropriate support regime was in effect.

"When the offender is not taking his medication, there is a real chance of him transforming into a sexual predator," Justice Elkaim said.

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