The “incel” gunman who killed five people in Plymouth, England on Thursday reportedly had his gun licence returned to him by local police last month.

Jake Davison, 22, had his gun licence revoked last month following accusations of an assault charge two months prior. The killer is believed to have escaped punishment for the assault by taking an anger management course.

Family members are also reported to have contacted mental health professionals for help prior to the mass shooting in which the young man shot his mother, a three-year-old girl, and three other members of the public before turning his gun on himself.

Devon and Cornwall Police are now being investigated by the Independent Office for Police Conduct (IOPC) for their apparent failure in returning the gun licence — a requirement to own a firearm under the strict gun control laws in Britain — to Davison, according to a report from The Times.

The IOPC regional director, David Frost, said: “We will examine… the rationale behind police decision making, and whether relevant law, policy and procedures were followed concerning Davison’s possession of a shotgun. The investigation will also consider whether the force had any information concerning Davison’s mental health.”

While it has not been revealed whether Davison used the shotgun for which he had a licence, witnesses of the mass shooting claimed that he was wielding a “pump-action shotgun”.

The independent watchdog will also investigate whether police officers carried out their due diligence in regards to examining the incel killer’s mental state. Apart from pleas for help from his family, Davison was also active in sharing his struggles and his philosophy on his now-deactivated YouTube channel.

Breitbart London reported on Friday that videos from Davison included: ‘working on yourself” Lack of willpower drive and motivation when life beats you down, and Missing out on teenage love and experiences and people who say “its not a big deal”.

On this channel, the killer characterised himself as a “23-Year-Old Virgin Autist” in a post from mid-July. In the description of the video, Davison described the video as “venting about my life sorry for the pity party im not really looking for that but there is a lot more BS [bullshit] i dealt with in life that i didn’t mention [sic]”.

The mass shooting is not currently being treated as a terror incident, however the government and police are reportedly looking into whether his incel (involuntarily celibate) ideology was a motivating factor.

Home Secretary Priti Patel will look into cracking down on so-called incel groups and individuals, however it is unclear how organised — if at all — such groups are.

“I am very clear about this, we will always learn lessons from incidences, terrible tragic events like this — particularly where there are key factors, online activity for example, and you’ve already touched on another aspect such as the firearm itself,” Patel said.

“We need to find out the facts, let’s establish the facts behind this and, of course, we will work to do everything to make sure that if there are issues with the online space, post this incident we will look to follow that up,” she added.

During his twelve-minute rampage, Davison killed his mother and 43-year-old Lee Martyn and his three-year-old daughter Sophie.

He then went on to attack Ben Parsonage, 33, and his mother, Michelle Parker, 53, both of whom survived. Davison then shot Stephen Washington, 59, who was walking his dog, and Kate Shepherd, 66, who died later in hospital.

Follow Kurt Zindulka on Twitter here @KurtZindulka