In her mind's eye, Elise Schwarz can vividly conjure up a series of heart-wrenching snapshots. Running breathlessly through the streets towards her New York apartment. The state of disarray that greeted the Glasgow-born lawyer in the empty rooms. The firm tone of the nurse on the phone from the nearby hospital who urged Schwarz to get there as quickly as possible.

The paramedic that gently led her away while doctors worked to resuscitate Schwarz's infant son. The jarring moment when the diagnosis for Evan, only five months old, was delivered: shaken baby syndrome.

Schwarz had left Evan in the care of a nanny when she went to work. In the weeks that followed, as Evan fought for his life and she kept a 24-hour vigil at his bedside, the agony was further compounded as child protection services looked to point the finger at Schwarz and sought court action to remove custody of her son.

"There were times when I almost didn't keep going," she says. "I had this image of holding on by the skin of my fingernails. That is how tenuous my grip on sanity felt. I could have gone over the edge at any point."

The glittering life in Manhattan behind her, Schwarz, 45, has returned to Scotland. In the living room of her mother's house on a pleasant street in the south side of Glasgow, photographs of Evan line the mantelpiece. In each his bright blue eyes and shock of wavy blond hair stand out amid the tangle of tubes and ventilators.

It is two years this month since Evan passed away in his mother's arms. The story of his tragically fleeting life is documented in a book, I Believe in Evan, which Schwarz wrote based on diaries and journals she kept at the time. She insists it isn't about apportioning blame or a fight for retribution, rather her way of keeping his memory alive.

Schwarz had moved from Glasgow to the US in her twenties, seeking adventure. She lived in San Francisco and later moved to Washington DC to attend law school. After graduating, Schwarz passed the New York bar exam and by her mid-thirties was an established attorney amid the cut and thrust of the city's fast-paced legal scene and a partner in her own firm.

Having long wrestled with her sexuality, it wasn’t until she was 31 that Schwarz felt comfortable enough to come out as gay. At 38 and single, her yearning for motherhood became so intense that she opted for artificial insemination.

Schwarz remembers the sheer delight at discovering she was pregnant with Evan. “I had a fantastic pregnancy – absolutely wonderful,” she says, smiling softly. She describes Evan’s birth in a Manhattan hospital on September 3, 2011 as “the happiest day of my life”, the rush of affection palpable in her voice when recalling the easy-going, smiley baby who lit up her world.

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As her maternity leave drew to a close, Schwarz hired a nanny based on the recommendation of a friend. Norma came with glowing references from previous employers. Schwarz met and liked her. It seemed an ideal fit.

They settled into a comfortable routine with Norma looking after Evan between 8am until 6pm while Schwarz returned to work as a commercial litigation and immigration attorney. Yet, there were early ripples in the seemingly perfect tranquility. In the weeks leading up to Evan being admitted to hospital, there had been two other incidents, both times Norma raising the alarm.

The first time Schwarz received a panicked call to say Evan was turning blue. He was checked over in hospital and released. The second time, Norma said she thought Evan was having a seizure. A doctor who examined Evan concluded this wasn’t the case. He instead believed that Evan had been breath-holding in a bout of temper and insisted there was no lasting harm.

Schwarz was flooded with relief. A fortnight later, however, a text from Norma flashed up on her phone as she ran errands on her way home from the office. It read: “Can you please call me, Evan is holding his breath for a really long time.” Schwarz remembers running blindly to her apartment only to discover that Evan had already been taken to hospital.

The paramedics worked to resuscitate Evan but he was unresponsive. By the time Schwarz saw her son he was in a coma and had been placed on a ventilator. He was transferred to an intensive care unit (ICU). A shadow of pain crosses her face. “I still get flashbacks, but it is difficult to go in too deeply and think about what happened,” she says.

Events dramatically unravelled. As the nature of Evan’s condition became apparent – a severe head trauma leading to swelling and bleeding of the brain coupled with a retinal haemorrhage – all the evidence pointed towards Norma. Schwarz recalls meeting with an NYPD detective who promised her: “I want you to know that, if I can, I will do everything possible to bring this woman to justice.”

The police never doubted Schwarz was innocent. Yet, any small comfort was wrenched away when the Administration for Children’s Services (ACS) – the New York equivalent of child protection services – sought to remove Evan from Schwarz’s custody leading to six months of court hearings. After much protracted anguish, described by Schwarz as a “horrendous emotional experience”, she successfully battled the petition.

When charges were eventually brought against Norma at the New York City Family Court, she accepted a finding of child abuse. Her name was added to the Central Registry as a child abuser and Norma was banned from working with children for 28 years.

While the police had probable cause to bring criminal charges, the likelihood of conviction was too slim on account of the existence of only circumstantial evidence. To date, no criminal charges have been brought against Norma.

Schwarz is remarkably devoid of any bitterness as she speaks about her former nanny. For her peace of mind, she admits, it is vital to tell herself that Norma meant no deliberate harm.

“What I think happened is that he had a bad seizure and stopped breathing,” she says. “I don’t know, but in her panic, she may have shaken him which is awful and devastating. If that’s what happened, then she is not the only factor in this.

“Obviously, a huge amount of me thinking that is because I have the luxury of not knowing. I’m able to decide for myself that it wasn’t malicious – that she didn’t do it deliberately. When you think about her references and how I feel she conducted herself throughout, I’m comfortable with assuming that is what happened. I trusted her independently of everything else.”

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She hasn’t seen Norma since that final day in court. “For what I think she did I forgive her,” says Schwarz. “Even if it was the worst case scenario, I believe I forgive her because she’s not relevant in mine and Evan’s life and hasn’t been for a long time. I don’t need to think about her.”

Yet, the months of legal battles coupled with the unrelenting worry of her son’s grave condition, took their toll. Evan had remained unresponsive, his tiny body lying still and quiet beneath the tubes and wires that snaked from a multitude of blinking, beeping machines.

Schwarz’s belief that her son would recover didn’t falter. Even when the doctors broached the subject of withdrawing care, saying that Evan was “about as brain dead as you can be without being brain dead”, she remained resolute, putting up photographs from happier times around the hospital room to remind staff of how much the little boy in their care was loved.

After four weeks in ICU, Evan was moved to a long-term care facility in upstate New York. Schwarz spent the next nine months camped out there, curling up each night on a couch at her son’s bedside. Despite the bleak prognosis, she refused to give up, feeling bolstered by every movement, no matter how small, and buoyed each time Evan opened his eyes to gaze up at her.

When Evan was stable enough to be transferred, Schwarz chose not to return to New York but instead to Glasgow. Evan was admitted to the former Royal Hospital for Sick Children at Yorkhill in December 2012. Schwarz recalls happy hours spent with her son at nearby Sense Scotland in Kinning Park, where Evan responded well to music and sensory room sessions.

“The best signs came here in Scotland because Evan thrived,” she says. “He had quite significantly come out of his coma by that time. He definitely got my vibe. I was more relaxed and sleeping better. It was better in all kinds of ways.”

By the summer of 2013, Evan’s condition had improved enough to spend a few days each week at home with Schwarz. That September, he was allowed to leave hospital. For Schwarz, it marked the realisation of the dream she had clung to in her darkest hours.

But less than six months later, Evan took ill again. His temperature spiked and he was re-admitted to hospital. Despite the valiant efforts of doctors, Evan’s condition deteriorated and his heart began to fail. He passed away in his mother’s arms aged just two-and-a-half.

A faraway look comes into Schwarz’s eyes as we sit quietly in her mother’s living room, the only sound that of heavy rain lashing the window and the wind howling around the house. Her voice cracks as she recalls holding Evan in those final moments. “I was there with him,” she says. “Much as it was an awful day and I wish it hadn’t happened, I feel fortunate in a lot of ways for the way it did.

“There was nothing anyone could have done. I can’t fault anyone for anything that happened. He died as safely as possible. Every aspect was accounted for. He was in with the best doctors and thoroughly cared for. They did everything they possibly could.”

Since returning to Scotland, Schwarz has stayed in the family home she grew up in as the youngest of five children. She lives with her mother, Pat, 85, a retired secondary school English teacher. Her late father, Tony, a GP, passed away in 2011 when Evan was only a few weeks old. “I tell people that I look after my mother but that is bullshit,” she says, with a wry smile. “She looks after me.”

Schwarz has requalified to practice law here but has yet to return to work. “I loved being a lawyer but to be a good lawyer you have to throw yourself fully [into your cases] to help other people and I don’t have that inclination or energy at the moment,” she says. “I feel a little bit stronger now than I have done in the past, but whether that will wax and wane, who knows?”

Grief, she concedes, is a complicated beast. “You learn to stop fighting it because it is always going to be there,” she says. “It is not always painful. You have a run of good days, but then on others it is incredibly sore. I’m always waiting to see if there is a pattern but there is not.

“I drew myself a chart of grief which is almost like a compass. Down at the bottom is ‘struggling to cope’ and at the top is ‘full of love and pride for Evan’. When I’m struggling to cope, I know I will be back at the top at some point which does help.”

While Schwarz has made the decision to speak publicly about her life with Evan, it never fails to amaze her how people – “emotional vampires” she calls them – want to feast on her grief.

“There is a boundary and some people are very respectful,” she says. “But then there are other people who want to touch the wound again and again to see how sore it can be for you. Not because they want to hurt you, but they want to take the pain and see what it feels like.”

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Yet, Schwarz remains sanguine about the rationale for sharing her story. “People often ask if whether the reason I’m doing this is to raise awareness and to stop it from happening again,” she says. “The honest answer is no, that’s not why I wrote the book.

“It was such a specific set of circumstances, how could those happen to anyone else? It would be disingenuous to say I did this for other people. I wrote this book mainly for me, but also a huge part for Evan so people know how wonderful he is.”

“It didn’t start out as a book,” she adds. “It began as a way to vent, my way to try to process what was happening and get a tiny bit of control in an uncontrollable situation.

“I naively thought that if I wrote a book I would never need to talk about it again. There are some flashbacks I can’t stop, but there are others where I can tell myself: ‘It’s OK, you have written that down – you don’t need to relive it again.’ That is therapeutic.”

Evan hasn’t remained as a toddler in her mind, rather Schwarz can picture him growing as the months and years pass. “I think of him as being four-and-a-half now,” she says. “It was painful to see other children of his age when he passed away, but that is fading now.”

Most days, says Schwarz, she sets aside time to think about her son, looking at his photograph and talking tenderly to him. “In the early days, the grief was so heavy that I couldn’t connect with the love,” she says. “Now that the grief is more manageable, I don’t love him any less than I ever have.

“There are obviously still times when it is difficult but I think I have come out the other side of that. I will never not have Evan in my heart. His light won’t ever fade.”

I Believe in Evan by Elise Schwarz is published by John Blake, priced £7.99. To make a donation to Sense Scotland, visit justgiving.com/elise-schwarz