HALIFAX -- She sat motionless in the wood-panelled, windowless courtroom as the judge delivered the sentence: Life in prison with no chance of parole for a decade.

Lindsay Souvannarath was then led away by sheriffs, returned to the jail cells that have been her home since 2015.

It's been three years since the Chicago-area woman was arrested at the Halifax airport with a "death suit" and books on serial killers in her luggage.

She was planning a Valentine's Day shooting rampage, a plot concocted online with a Halifax teen that would have seen them open fire at the Halifax Shopping Centre food court on a busy Saturday in February 2015.

The 26-year-old American pleaded guilty to conspiracy to commit murder only after thousands of damning Facebook messages between the conspirators were deemed admissible as evidence in the case.

Nova Scotia Supreme Court Justice Peter Rosinski told the court Friday that Souvannarath continues to pose a threat to public safety.

The judge said she has not expressed remorse for her murderous plot, nor has she renounced her ideological motivations for the conspiracy.

In his decision, he called her prospects for rehabilitation "very questionable" and said she needs to be separated from society until safety concerns can be addressed.

Rosinski said he is satisfied that had the plot not been interrupted by an anonymous tip and the quick actions of local police, the plan would have been carried out.

"Coming upon unsuspecting members of the public at the mall that day, what carnage would they have inflicted with a 16-gauge shotgun with 23 shells; a .308 calibre lever-action rifle with 13 shells; and a knife to finish off the wounded?"

The judge added: "Ms. Souvannarath's intention was to kill more than the 13 people who suffered that fate at the Columbine High School shooting," he wrote, referring to her obsession with the massacre in Littleton, Colo.

Her co-conspirator, 19-year-old James Gamble, killed himself as police surrounded his Halifax-area home.

Kate Battan, the lead investigator of the 1999 shooting who wrote a report highlighting parallels between the school shooting and the mall plot, called it "ironic" that Friday's sentencing took place on the 19th anniversary of the Columbine shooting.

She spent a month combing through the private online messages between Souvannarath and Gamble and their plans to mount an attack at a Halifax mall.

"My impression is that they were all in and this was not a joke," she said in an interview. "At some point this became real, this was going to happen."

The judge shared that view, telling the court that the "plan had been set in motion" once Souvannarath boarded a plane for Halifax.

The spectre of shooters opening fire in a busy mall threatened thousands of shoppers and workers and unsettled the city for months.

Rosinski cited the explicit intention to create mass panic and undermine the community's sense of security as an aggravating factor in the sentencing.

"They intended to maximize dead and wounded casualties," the judge wrote in his 32-page decision.

"That they intended to be mocking, callous and brutal in their treatment of potential victims they encountered is an aggravating factor."

He said his sentencing was in part shaped by the principles that apply to terrorism offences and is intended to "send a clear message" to those conspiring to kill multiple people.

"Those who choose to pursue such deadly plans will pay a very heavy price," Rosinski wrote.

Crown attorney Mark Heerema said the sentence serves as a deterrent for similar crimes.

"The court was unequivocal that this kind of conduct here in Canada by an offender who is not claiming to be remorseful or renouncing will never be accepted," he told reporters outside the courtroom.

The woman from Geneva, a quiet suburb of Chicago, has been ordered to provide a sample of her DNA and will be subjected to a firearms prohibition for 10 years after her release from prison. He gave her credit for three years served in custody, so she will be eligible for parole in seven years.

Although the judge has recommended intensive psychological and psychiatric counselling and treatment, the sentence of life in prison means the 26-year-old could spend the rest of her days behind bars.

A third accomplice -- a local man described in court as the "cheerleader" of the plot -- was previously sentenced to a decade in jail.

At the sentencing hearing earlier in the week, Rosinski asked Souvannarath if she would like to address the court. She said: "I decline."

Before delivering his decision Friday, the judge entered letters from Souvannarath's parents and grandparents as exhibits in the case.

The parents of both Souvannarath and Gamble were in court for the sentencing hearing, but declined to be interviewed.

Souvannarath has been held at the Central Nova Scotia Correctional facility in a Halifax-area industrial park since her arrest. Her lawyer has said she will likely be transferred to a women's institution in southern Ontario after sentencing.

The judge noted that the college graduate has been called a quiet prisoner who keeps to herself, participates in Books behind Bars, and was enrolled in a humanities course offered by Dalhousie University.