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Mackenzie, who lives with his parents in the nearby village of Cardross, suffers from a myopathy, which has robbed his tiny frame of muscular support, as well as autoimmune enteropathy, a rare and delibilitating gastrointestinal disease that causes his immune system to attack his intestinal wall.

So poor was his health that Mackenzie spent most of his weekdays last spring at Yorkhill Royal Hospital for Sick Children, where a specially modified chair provided him with some comfort. At weekends, however, the device had to stay in Glasgow, meaning the youngster had to be strapped into his pushchair.

Within 24 hours, Mr Sharkey, 55, was on the phone to Mackenzie’s mother, Kelly. “He explained he heard about my son through word of mouth, but that he wanted to help,” she recalled.

“He said he didn’t think it was right that Mackenzie didn’t have a chair at home, and I was thrilled at what he had planned.”

In a matter of weeks, Mr Sharkey had arranged a fund-raising evening in Helensburgh’s Coopers Bar, with entertainment and local bands – including the Midget Millers, a Frankie Miller tribute band he fronted – to help generate the necessary £1,300.

“Tommy just tracked us down off his own back,” Mrs Cameron added. “No one asked him to hold a charity night – he decided to do it because he thought Mackenzie deserved better.”

It was a small gesture of kindness – commended by local MSP Jackie Baillie in a motion to the Scottish Parliament – which, as many people in Helensburgh will testify, typified Mr Sharkey’s altruism.

Little over a year later, however, a solitary act would destroy the lives of his family and those around him.

In the early hours of Sunday, 24 July, residents in Scott Court, a quiet street a stone’s throw from Helensburgh’s picturesque seafront, heard a young girl’s screams shatter the silence. It was eight-year-old Bridget Sharkey, Tommy’s only daughter.

Just after 5am, a blaze tore through the property’s living room, thought by police to have been started deliberately. With the only exit blocked by flames, those inside were trapped.

There would be just a single survivor – Angela Sharkey, Tommy’s wife. Her children died: Bridget, and Thomas Jnr, a 21-year-old promising golfer on a trip home from his scholarship at Georgia Southern University.

Their father had been able to climb on to a windowsill, but suffered severe burns and died in Glasgow’s Royal Infirmary six days later after he had been informed of his children’s deaths.

In the aftermath, Angela was so heavily sedated that she thought she was speaking to her son in the burns unit of the Royal Infirmary, and refused to believe her sister, Margaret, on being told her family was dead.

On realising the full horror of what had passed, she made an emotional appeal. “The three things I loved most about my life are dead,” she said. “I don’t know how somebody can carry on with their life knowing that they’ve done this.”

Nearly two months have passed since the fire, yet the widow’s heartfelt appeal has gone unheeded, with no arrests made.

Mrs Sharkey is recuperating while the bodies of her husband and children have not yet been released by investigators, meaning that their funerals have been unable to take place.

On the streets on Helensburgh, where Mr Sharkey played such an active part in community life, it is a frustrating and disconcerting situation which has come to impact on everyone.

“People in Helensbugh are still shocked at what happened. There’s a great sense of sadness for the family and the fact this could happen in such a small community,” said Vivien Dance. “The fact no one has been arrested means that the town is struggling to come to terms with it.”

A family friend of Mr Sharkey for more than 40 years, Ms Dance supported him in his charitable efforts. “We’re desperate for an arrest to be made,” she added. “People you speak to in Helensburgh are still reeling from the horror of the deaths.”

Most perplexing of all is the motive for the triple murder. Numerous theories have been made in recent weeks, with some suggesting that Mr Sharkey was a police informant.

Certainly, few would dispute that Mr Sharkey had at times lost his way in life. He was sentenced to 18 months in prison in 1995 for cannabis cultivation. Two years ago a pub he ran, the Mariners, burnt to the ground. No-one has been apprehended in connection with the incident.

As recently as February, he was the subject of an attack which left him with multiple stab wounds. The case, where the alleged assailant was known to Mr Sharkey, has yet to come to court, prompting notions that the fire was the consequence of a family feud.

Father Peter Lennon, of St Joseph’s Church, who has helped console “fantastically strong” Sharkey family following the fire, agreed: “Mr Sharkey had a chequered life as a young man, but I think when he met Angela things took a turn for the better and he became a changed man.”

As well as helping raise awareness of Mackenzie Cameron’s condition, Mr Starkey helped other youngsters. One such drive was for Aedan McGinley, a toddler with a congenital heart condition. In 2007, Mr Sharkey rallied a committee to stage a concert in the hope of raising £9,000. In the end, however, the total reached £23,000.

He was a man with a past, but who strove for a better future. “Tommy said he had two ambitions in life,” Fr Lennon explained. “To see his son play in the Scottish Open and to walk his daughter down the aisle.”

But with the death of Tommy Sharkey, it was not only his dreams that ended. “Mackenzie was in hospital unwell when we got the call about what had happened to Tommy and his family,” Mrs Cameron revealed. “I was absolutely devastated, and I think everyone is.”