LONDON — A 22-year-old who posted YouTube videos filled with despair and self-loathing is suspected of killing five people, including his mother and a 3-year-old girl, in the first mass shooting in Britain in more than a decade, police said.

Thursday night’s shooting rampage in the seaside city of Plymouth, in southwest England, stunned the country, which has some of the toughest gun laws in the world.

Police confirmed that the suspect, identified as Jake Davison, held a license for the gun used.

According to the police account, Davison started firing his weapon on Thursday evening around 6 p.m. local time inside a modest two-story brick home. His first victim was his mother, Maxine Davison, 51, also known as Maxine Chapman.

Davison then ran out onto Biddick Drive and killed the toddler, Sophie Martyn, and her father, Lee Martyn, 43. Davison shot at two other passersby, who were badly injured, before he entered a park and shot Stephen Washington, 59, who died at the scene, and Kate Shepherd, 66, who died at a nearby hospital, police said.

Davison turned the gun on himself, taking his own life, before firearms officers could tackle him, Devon and Cornwall Police Chief Constable Shaun Sawyer said at a news conference Friday.

Police said they were at the scene within six minutes of being alerted and that there had been multiple witnesses to the multiple killings.

There was no immediate, clear motive, Sawyer said on Friday. He added that authorities were not considering terrorism or any far-right associations as the spark, though officers were examining the suspected gunman’s computer for clues.

“We believe we have an incident that is domestically related, that has spilled into the street and seen several people within Plymouth losing their lives in an extraordinarily tragic circumstance,” Sawyer said.

Police did not say whether Davison had mental health issues.

Britain’s home secretary, Priti Patel, who is in charge of domestic security, called the killings “absolutely tragic and devastating” and suggested she would seek answers as to why Davison had a gun license.

“There will be a range of questions that will inevitably be asked,” Patel said.

The Independent Office for Police Conduct, an accountability agency, said in a statement that it would investigate the suspect’s gun-licensing history and his previous contact with police. Regional director David Ford said it had not been established whether a shotgun that had been confiscated but returned to Davison had been the one used Thursday, but that his office would examine police decision-making, including whether officers had appropriately considered any information about Davison’s mental health.

Davison’s Facebook account and YouTube account were removed by the platforms. But British news media aired video clips he had posted to YouTube in the days before the rampage. In one of segments, he complained, “I’m so beaten down and … defeated by life.”

In an expletive-filled rant, he said: “I tried and I’ll always keep trying, but I’m at the point now where why do I even bother? For what? I’m still in the same house, the same situation, same position … everything’s still the same … for the most part its just been me against the world … fighting an uphill battle …”

At one point, he referred to “The Terminator” movie franchise, where “everything’s rigged against you” and “there’s no hope for humanity.”

The BBC reported that in one video, Davison “made references to ‘incels’ — the misogynistic online groups of ‘involuntary celibate’ men, who blame women for their sexual failings and who have been linked to a number of violent acts around the world.”

Davison worked as an apprentice for Babcock International, a defense company that serves the British navy and is one of the largest employers in Plymouth.

“My thoughts are with the friends and family of those who lost their lives and with all those affected by the tragic incident in Plymouth last night,” Prime Minister Boris Johnson tweeted Friday as he thanked emergency responders.

Unlike in the United States, mass shootings are extremely rare in Britain, which has one of the lowest gun homicide rates in the world and some of the strictest gun laws, including comprehensive background checks.

The country’s deadliest mass shooting was in 1996, when a gunman killed 16 children and their teacher and injured 15 others in Dunblane, Scotland. That massacre is widely regarded as a dark stain on British history that led to an overhaul of gun laws. The government pursued legislative bans on assault rifles and handguns and made it harder for people to obtain other weapons.

Before Thursday, Britain had experienced only one other mass shooting since Dunblane. In 2010taxi driver Derrick Bird killed 12 people and injured 11 others in the Lake District in northwest England before killing himself. Criminologists noted that the rampage in 2010 might have been far more deadly if the taxi driver had been able to access stronger firepower.

Luke Pollard, a lawmaker for the area of Plymouth, Sutton and Devonport, said Thursday’s shooting was “unspeakably awful.”

“A very grim day for our city and our community,” he tweeted Thursday night.

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