A 22-year-old who killed his mother and four others wanted to kill two teenagers who taunted him about his weight almost a year before the shooting.
Jake Davison, a trainee crane operator, had assaulted two teenagers in an argument about being called fat in September 2020.
Darren Wood, the partner of Mr Davison’s mother Maxine, told an inquest that he was “raging angry” and had begun loading his pump-action shotgun after the incident in which he punched a boy and pushed a girl.
“He had come back from the park and they had been taking the p**s out of him,” Mr Wood told the hearing in Exeter.
“You could see he was angry, and you could feel the anger coming out of him. He came back and ran upstairs. Maxine went upstairs and I could hear him saying, ‘I’m going down there [to] kill them’.
“He said he was going to go back to the park and he went to his room to get his gun out the cupboard. I could hear something being loaded.
“Maxine was saying he couldn’t take that up the park and she said if he took it up the park he would be getting a jail sentence. She calmed him down.
He added: “I said to Maxine she should report it but at the end of the day she didn’t want me to report it – I wish I had.
“He was an adult and had assaulted a minor and he should have been charged.”
Mr Davison later handed himself into police after CCTV images of a suspect wanted for the assaults were circulated as part of a public appeal.
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His firearms certificate and weapon were later seized by police but returned in July the following year – just a few weeks before the deadly shooting in the Newham area of Plymouth.
The court heard that Mr Wood was in a relationship with Mrs Davison from July 2020 and lived with her between August and November 2020 before moving out.
He said the atmosphere in the house was “tense” and there were regular arguments between Mr Davison and his mother.
“She was scared of Jake for the best part of her life. He treated her like a slave – it wasn’t the mother and son relationship,” he said.
“It was brutal some of the things I used to see.
“She didn’t want him to have the gun. She rang the police up trying to get the gun taken away and trying to get him to sell it.”
On 12 August 2021, Mrs Davison, 51, was shot dead followed by Sophie Martyn, three, her father Lee Martyn, 43, Stephen Washington, 59, and Kate Shepherd, 66 before Mr Davison turned the gun on himself.