As a deaf person, he had experienced depression and a brief breakdown himself, and knew of other deaf people who had had suicidal thoughts.
One of them received no support, he says, and later took their own life.
According to various pieces of research, people in the deaf community are statistically between 25% and 50% more likely to suffer from mental health problems than their peers.
The reasons aren't known for sure, but some researchers believe communication problems, subsequent problems with peer relationships or difficult family dynamics can contribute to the increased risk. A link between deafness and central nervous system damage may also have an effect.
While Scotland's national Choose Life strategy has been offering training in suicide prevention for seven years now, Mr McCusker realised there was a problem. "The deaf community is a very small community, so almost everyone knows each other," he said.
That might make it doubly difficult for people to open up about their problems, he feared. "It can be difficult creating trust, confidentiality."
But he persevered and has now become Scotland's first deaf trainer under the SafeTALK programme and is equipped to train others.
Training materials including a DVD have now been prepared in British Sign Language (BSL) and subtitled versions.
SAFEtalk is aimed at giving professionals and members of the public the skills to intervene and provide practical help if those they know or work with are having thoughts of suicide.
It allows the person trained to recognise when someone else might be having thoughts of suicide and give them the confidence and skills to engage that person in direct, open conversations about suicide.
By listening and taking their thoughts and concerns seriously, the person can advise them and help them connect to someone trained in suicide intervention. Demand for the course comes not just from people working in settings such as mental health, primary care, accident and emergency or those working in care and support of vulnerable groups such as addicts.
Through the Read Between The Lines initiative, members of the public are also being encouraged to recognise warning signs and do more to help stop those who may be suicidal.
As a result demand also comes from the general public and demand from the deaf community in Lanarkshire has led to the setting up of a BSL SafeTALK session in Lanarkshire this month.
"The training is a short three hour session to ensure members of the deaf community have an understanding of what suicidal thoughts are and how important it is to ensure good support can be in place for those who have them to get effective treatment," Mr McCusker explains.
Alana Atkinson, programme manager for the Choose Life national initiative, said there were lots of things people could do to intervene if a friend or relative is having suicidal thoughts.
"It is a myth that by talking about it you will put the idea in someone's head when they didn't have it before. People are usually relieved others care enough about them to have that conversation.
"We know there is not just one thing that works and there are a range of interventions which we know can help."
People come forward to take up the SafeTALK training for a variety of reasons, often quite personal, she said. "Many of us in Scotland have been touched by the death of someone by suicide. People are motivated because they wish they understood it better, and had the skills and confidence to do something sooner."
The launch of suicide prevention week on September 9th will see the public encouraged to find out more, while the Scottish Government is expected to launch a new suicide prevention strategy later this year. "Suicide is important to us and we want to make sure we have done everything we can to stop people dying by suicide," Ms Atkinson said. "It is preventable and anyone can help."
Mr McCusker is looking forward to running the first group training for deaf people in Lanarkshire shortly and he also wants to encourage more people to come forward. "It is difficult to get hard evidence on suicide and the deaf community since death certificates do not record whether a person is deaf," he said. "But it is important to be aware that the deaf community are 25% more at risk of mental health problems. Awareness raising about the SafeTALK training and encouragement for more deaf trainers to sign up is needed," he said.