The man who killed Catie Miller and dismembered her body was arrested early in the police investigation because his appetite for murdering women was so strong, officers feared he would carry out his fantasies again.

Jason James Johnson was captured on wiretaps talking "about his desire to become a notorious killer" and that he "would like to kill again before he gets arrested," according to an agreed statement of facts presented Thursday in Nova Scotia Supreme Court.

Johnson, 31, and his girlfriend, Kelly Amanda MacDonald, 35, pleaded guilty to second-degree murder in Miller's death.

The court was told Miller, a mother from Dartmouth, pleaded with her killers to spare her life before she was beaten and stabbed to death on July 15, 2014.

Life in prison

The pair were both sentenced to life in prison. Johnson must serve 20 years in prison before being eligible for parole; MacDonald must serve 16. Both were handed five years for interfering with human remains — a term that will run concurrent to the murder sentence.

Miller, a 29-year-old mother of a young son, was dismembered and much of her body was found in Lawrencetown, according to the agreed statement of facts. She and Johnson had previously been in a relationship.

John Miller, Catie's father, told reporters outside the courtroom that his family felt a "very small degree of relief" that they did not have to sit through a trial.

John Miller, Catie's father, thanked the police for their efforts in closing his daughter's murder case. (CBC)

"We do not know why this occurred. It was a senseless and horrific murder. This should never have happened. Catie should not be dead. My grandson should have his mother," Miller said, his voice breaking.

"This is tragic beyond belief."

'Inherent dangerousness'

Johnson and MacDonald were charged with first-degree murder, but pleaded guilty to second-degree murder.

"There were many opportunities to let Catie Miller live," Justice Patrick Duncan said as he passed the sentence, adding "there is an inherent dangerousness in Mr. Johnson."

He said the couple "lacked the most basic humanity" and showed "extreme callousness and total disregard for human life" when Miller was "assaulted viciously before she was killed."

Duncan said MacDonald is as guilty as Johnson, even though she did not do the actual killing. Both were described in court as drug and alcohol abusers.

Jason Johnson pleaded guilty to second-degree murder in the death of Catie Miller and boasted he wanted to kill other women as well. (CBC)

Miller was reported missing by her mother on July 21, 2014. Police found video surveillance footage from a Bedford grocery store that showed her getting into Johnson's car.

Police began tapping Johnson's phone on Aug. 29, 2014, and what they heard was so disturbing, they believed they had to take the man into custody before he committed another murder.

'Mounting concerns'

Johnson attempted to convince an associate "to help him plan the kidnapping and murders of multiple females," the statement of facts said.

"Mr. Johnson became excited during these intercepted conversations and provided details of the manner in which he would like to commit these further murders."

He was arrested "out of mounting concerns by police that Mr. Johnson would follow through on his fantasies to kill again."

MacDonald's involvement in the murder began after a "panicked" call from Johnson who told her had beaten Miller. She later told an undercover police officer she and their child got into Johnson's car, where Miller was trapped in the trunk and still alive.

With MacDonald at the wheel, they travelled to Lawrencetown to drop off the child with MacDonald's mother.

On the drive, Miller regained consciousness and "started screaming and kicking in the trunk and yelling 'Jason' and 'You don't have to do this,'" according to the agreed statement of facts.

'Finish her off'

"Ms. MacDonald feared that Ms. Miller would kick out a tail light and she told Mr. Johnson that they had to 'finish her off.'"

After dropping off the child, the couple headed toward Sheet Harbour and Miller continued to kick and make noise in the trunk. Twice they stopped and Johnson stabbed Miller. The second attack was fatal.

The statement of facts also outlines gruesome details about how the two disposed of Miller's body. Police eventually recovered a number of body parts, which were identified as Miller.

'My heart cannot find rest'

In a victim impact statement, Miller's mother said Thursday she has felt helpless and hopeless since her daughter died.

"My heart cannot find rest. The colour is gone," said Terry Miller.

She added that her grandson started school this year without his mother to walk him there.

Neither Johnson nor MacDonald showed any emotion as the family impact statements were read. Sobbing could be heard throughout the courtroom.

Johnson did not speak, but MacDonald addressed the court and said she was "very sorry."

"There are no words that I can say for either of you to forgive me for taking Catie's life," she said. "I just hope that one day that God chooses to forgive me on your behalf."

3 properties searched in investigation

Miller's disappearance was a missing persons case before police classified it as a homicide.

As part of their investigation, police searched three properties in Lawrencetown, Goffs and Sheet Harbour Passage. Miller's remains were found in one of those locations.

Her parents launched a high-profile search for her while she was still thought to be missing.

Miller grew up in Bedford and attended King's Edgehill School in Windsor. She studied at Saint Mary's University and later the Nova Scotia Community College, where she trained as an electrician.