A 22-year-old man suspected of killing three people at a shopping centre in Denmark's capital Copenhagen is due to appear before a judge for questioning.
Two Danish citizens, both aged 17, and a 47-year-old Russian citizen were killed in Sunday's attack.
The suspect had mental health issues and there is no indication of a terror motive, police say.
He had a rifle and a knife and his shooting was random - "not motivated by gender or anything else" - they said.
Speaking to reporters on Monday, police chief Soeren Thomassen said they believed the suspect - described as "an ethnic Dane" - was acting alone and was not helped by anyone else.
He added that the suspect was known "peripherally" to police.
Police are also investigating videos of a young man with weapons which have been circulating on social media since Sunday, and believe them to be authentic.
Four people were wounded in the attack.
Two are Danish citizens - a 40-year-old woman and a 19-year old woman. The other two are Swedes - a 50-year-old man and a 16-year old woman.
One remains in critical condition, the chief physician at one of the hospitals treating some of the victims said, giving no further details.
In total, 30 people were injured during the attack, police said.
The deadly attack began at Field's shopping mall at around 17:35 (15:35 GMT) local time on Sunday, according to police reports.
The multi-storey shopping centre - one of the biggest in Denmark - is near a secondary school as well as a large student housing block, and is often full of young people.
Several of those present at the shopping centre spoke of how they fled the scene or hid in toilets, shops and storage rooms.
One of them, named Isabelle, told Danish media: "Suddenly we hear shots - 10 shots I think - and then we run through the mall and end up in a toilet, where we huddle together in this tiny toilet, where we are around 11 people.
"It's really hot and we wait and we are really scared. It's been a terrible experience."
Police arrested the suspect near the mall - 13 minutes after being alerted to the attack.
Less than a mile from the shopping mall, British singer Harry Styles was due to perform at a 17,000-capacity venue where crowds had already gathered inside before the show was cancelled.
Fans - many in their teens - were escorted by police to underground stations where parents picked them up, Danish media report.
The suspected gunman will appear in court charged with manslaughter on Monday, though no time has yet been given for when he will appear.