Figen Murray, whose 29-year-old son Martyn Hett was among the 22 killed in the blast three years ago, said she went into “self-preservation” mode while sat in the Old Bailey, just metres from Hashem Abedi during his trial earlier this year.
The Manchester-born defendant, younger brother of suicide bomber Salman Abedi, was convicted of 22 counts of murder, one count of attempted murder encompassing the remaining injured, and one count of conspiring with his brother to cause explosions, during his trial in March.
But he effectively withdrew from the process by refusing to leave his prison cell, sacking his legal team, and then ordering no closing speech be made in his defence.
It meant Mrs Murray, the survivors, and the families of those killed and hurt in the blast were left without hearing from the man police believe may have masterminded the plot.
The 23-year-old is due to be sentenced at the Old Bailey over two days next week.
Mrs Murray told the PA news agency her Masters degree in counter-terrorism, which she enrolled on after the tragedy, was her “saving grace” during the trial as it allowed her to “put a professional head on”.
Speaking ahead of the sentencing hearing, Mrs Murray said: “I made a very conscious effort to go into a professional zone and that was maybe a coping mechanism I used.
“It helped me separate my emotion, from getting too upset in court.
“I sat there with a professional head on, I know it sounds weird. But I had to switch the emotions off.”
Mrs Murray said she “locked eyes” with her son’s killer “once or twice” during the trial, but tried not to think about the emotional impact of his actions.
“I just looked at him,” she said. “To be honest with you he looked like an ordinary young man who got it so horrifically wrong.
“I thought ‘shame on you’ and that’s all.
“I really tried very hard not to get emotionally engaged. It’s self-preservation at the end of the day.”
Mrs Murray, who will turn 60 next year, publicly declared days after the terror attack that she had forgiven the suicide bomber.
She maintains she has “no anger” for the Abedi brothers, despite Hashem failing to follow through on his commitment to police when he was extradited to the UK from Libya a year ago that he would co-operate fully with the investigation.
She said: “He didn’t take his chance to do so (assist), I have no idea why. I have no idea what was going on in his head.
“I trust the British legal system. Whatever the judge gives this person will be just punishment for a crime he committed.”
But Mrs Murray said the sentence will not bring closure for her.
“We as families have a life sentence – ours is until the end of days,” she said.
“As a mum, losing a child is the ultimate life sentence.
“That will never go away, that loss will never be filled, will never ease.
“All this nonsense about ‘time is a great healer’, it doesn’t apply for me at all.
“I’m sure in five or six years, 15, 20 years, I will feel that same void.
“Somebody asked me the other day if I will draw a line under this when court is finished.
“No, there is no line.”
Mrs Murray has been unable to return to her job as a therapist since the terror attack, instead ploughing her energy into her Masters and campaigning for Martyn’s Law, a requirement for all entertainment venues to have a strategy for dealing with terror attacks.
The Government’s Protect Duty, which builds on Martyn’s Law, had been intended to go to consultation this spring.
However, the coronavirus outbreak meant plans to canvass opinion among the leisure, entertainment and hospitality sectors have had to be put on hold.
Mrs Murray said she remains determined to see the campaign through, as a tribute to her son.
She said: “Whether it’s a distraction from my grief, I have a need now to be Martyn’s mum more than ever.
“Everything I do, I do with Martyn on my shoulder.
“He’s with me – I’m not religious – but he’s with me.”
A public inquiry into the bombing is scheduled to start next month.