Johnston (67), who has been diagnosed with terminal cancer, was yesterday sentenced to life imprisonment with a minimum non-parole period of 10 years.
His son, Owen, with wife Jo-Anne, outside court yesterday declined to comment on the sentencing but, on their behalf, Detective Sergeant Derek Shaw said it brought "some degree" of closure.
"For family and friends of Lesley there will probably never be complete closure because they'll have to live with Warren's decision and the consequences of it," Det Sgt Shaw said.
About 20 of Mrs Johnston's family members, friends and Roxburgh Health Camp colleagues were in court for her killer's sentencing.
As Owen Johnston read aloud his victim impact statement, a woman in the public gallery muttered "Bastard" in between sobs - an insult directed at the accused.
Johnston sat in the dock, occasionally shaking and crying.
His gaze fell upon his son and daughter-in-law often and at one point he mouthed a word to someone in the public gallery.
Mr and Mrs Johnston were stoic, succumbing to emotion only while reading out their victim impact statements.
They spoke about feeling helpless and angry, torn between worrying for Johnston's health and wanting to distance themselves from the murderer.
"Who gave you the right to rob my mother of her life?" he said to his father.
"Myself and my family haven't done anything wrong, so why are we the ones being punished?" Mr Johnston asked.
His wife is reminded daily of Mrs Johnston's absence, when she sat at her work desk beside where her mother-in-law used to sit.
"You had no right to do this. The hardest thing I've ever had to do in my life is sit down with Owen and tell our three children [aged 15, 12 and 9 years at the time] that their grandmother had been shot and killed," she said.
"If only you could have seen the look of shocked despair and sadness that was in their eyes," Mrs Johnston told her father-in-law.
She said her children felt unsafe, feared death and had trouble sleeping. She also mentioned her husband's strength and the wonderful support of family and friends.
Mrs Johnston said her mother-in-law's memory would be kept alive and she only wished Johnston had thought about the impact his actions would have before killing his wife.
Since March 14, 2009, Johnston and his wife had been grieving the loss of their only daughter who died of cancer in their home and under their care.
In February last year, Johnston became very depressed and the news his wife of 43 years no longer loved him, that she loved someone else, was in a relationship and was leaving him was unbearable. He was then diagnosed with a terminal illness, a malignant tumour in his lung.
On March 11, 2011, he stole a .22-calibre rifle from his son's home and wrote a suicide note before shooting his wife twice in the back as she ran from him. He then shot himself in the chest.
He recovered from his wounds and admitted a charge of murder.
In his suicide note, Johnston said if he could not have his wife, neither could her new partner.
Johnston's aunt, Beverly Stewart, a Dunedin resident, was also in court.
Mrs Stewart told the Otago Daily Times she did not approve of his crime but she would continue to support him.
