A police force is under investigation for alleged breaches of health and safety rules before the Keyham mass shooting, an inquest heard.

The Independent Office for Police Conduct (IOPC) has launched an inquiry into Devon and Cornwall Police’s firearms licensing unit.

Jake Davison, 22, killed his mother Maxine, 51, after a row and then shot dead four others in a 12-minute attack in Plymouth.

Three-year-old Sophie Martyn; her father, Lee, 43; Stephen Washington, 59; and Kate Shepherd, 66, all died on the evening of August 12 last year in the Keyham area of the city.

The apprentice crane operator then turned the pump-action shotgun on himself before armed officers reached him.

The killings happened just weeks after the shotgun and licence had been returned to him by Devon and Cornwall Police. They had been seized in 2020 after Davison assaulted two teenagers in a park.

He had applied for a shotgun certificate in July 2017 and after the application was processed a certificate was issued to him in January 2018 that was valid for five years.

As part of the IOPC investigation, two members of staff have been served with gross misconduct notices, while an officer has been served with a misconduct notice.

A pre-inquest hearing at Plymouth Coroner’s Court heard the watchdog has now launched a criminal investigation into the firearms licensing unit.

“At the conclusion of our investigation into the force’s granting of a shotgun certificate and later return to Jake Davison of a shotgun, we sought specialist legal advice and have since decided to conduct a criminal investigation,” an IOPC spokesman said.

“Our investigation will examine whether the Office of the Chief Constable of Devon and Cornwall Police, as corporation sole, may have committed any offences contrary to the Health and Safety at Work Act 1974.

“We have advised the force, the Police and Crime Commissioner, the coroner and families of our decision.”

Edward Pleeth, a barrister representing the watchdog, told senior coroner Ian Arrow the investigation would take some time but believed it would not affect next year’s inquest, which is due to begin in January.

“The IOPC has determined it is necessary to conduct that investigation,” he said.

“It is unlikely to be finished before the start of the inquest in January and the IOPC has undertaken to continue to provide your office with updates as the situation develops.

“IOPC investigations and any subsequent proceedings flowing from those play a central role in learning lessons and enabling those responsible to be held to account and it is in the public interest that these investigations, including this latest investigation, be able to reasonably run their course.

“We undertake to use best endeavours to ensure that this new investigation is completed as properly as possible, but it is likely as I say that a fair and comprehensive investigation will take some months and would not be finished before the start of the inquest.”

Jason Beer KC, representing the police, said he was not seeking to adjourn the inquests in light of the development as the force has committed through former chief constable Shaun Sawyer, who retired last month, to provide prompt answers to key questions.

“It has decided to start an investigation into some of the very matters that will be the subject of investigation and examination in your inquests,” he said.

“The families have described this position where the IOPC announced last Thursday that it was going to start its investigation as ‘far from ideal’.

“We’ve used the phrase ‘sub-optimal’. Both of them of course contain a very significant degree of understatement.”

Social media usage by Davison suggested an obsession with “incel” culture, meaning “involuntary celibate”, as well as an interest in guns and the US.

Reports have suggested Davison’s mother had been struggling to get help for her son, having become concerned about his mental health. A previous hearing has heard she had reported him to the counter-terrorism Prevent programme.

Assistance Chief constable Jim Nye said: “Throughout the last year the force has co-operated fully with the IOPC investigation, the coronial process and commissioned an independent review of the force’s firearms licensing procedures by Durham Police.

“We are aware of the latest developments from the IOPC investigation and continue to co-operate fully with them, while considering next steps the force may choose to take on this matter.

“The force notes this development is in its early stages and no determination in terms of potential corporate culpability has been decided.”

A further pre-inquest review will take place on December 19.