Jake Davison turned the gun on himself and committed suicide after gunning down five innocent people on Thursday evening.
He had been in contact with a mental health telephone helpline service in the city, run by the Livewell Southwest organisation, over the last 18 months, according to BBC News.
A spokeswoman said: “When mental health services were approached for help, it was given.”
She added: “The first response service continued throughout lockdown and was strengthened to help people who were struggling.”
Davison killed his mum Maxine Davison, 51, Stephen Washington, 59, and Kate Shepherd, 66, along with father and daughter Lee Martyn, 43, and Sophie Martyn, three during the rampage.
It comes days after it was revealed police failed to trawl through his social media accounts before giving back the gun because it was an “invasion of his privacy”.
Davison’s pump-action shotgun was handed back last month after it was taken from him in December 2020 following an alleged assault.
The apprentice crane operator described himself online as a “Terminator” and said he was “defeated by life” before killing his mother Maxine and four strangers.
He also wrote about his affinity with the “incel” movement, a highly misogynistic group of men who blame women for their involuntary celibacy.
The YouTube user posted online that he was “defeated by life”, as he blamed his troubles on not having a girlfriend.
A fortnight ago, the killer spoke of his affinity with the “incel” movement, which has been linked to a number of mass shootings in the US.
But in one of his videos Davison said he “wouldn’t clarify myself as an incel”.
His channel was subscribed to gun-related accounts and another named Incel TV, which features content related to “involuntary celibacy.”
Incel is an online subculture involves men who express hostility and extreme resentment towards those who are sexually active, particularly women.
Devon and Cornwall chief constable Shaun Sawyer said his force didn’t check Davison’s social media because they feared invading the 22-year-old’s privacy.
It is the worst gun massacre in the UK since taxi driver Derrick Bird killed 12 people in Cumbria in 2010.
Meanwhile, the Independent Office for Police Conduct (IOPC) has launched its investigation into Devon and Cornwall Police’s decision-making in relation to Davison’s possession of the weapon and certificate.