A gunman who killed three people when he opened fire in a crowded shopping mall acted alone and apparently selected his victims at random, Danish police said on Monday, all but ruling out that the attack was an “act of terrorism”.

Authorities filed preliminary charges of murder and attempted murder against a 22-year-old Danish man, who will be held for 24 days in a secure mental health facility while authorities investigate the crime, prosecutor Søren Harbo told reporters. Police have said the man was known to mental health services without elaborating.

The police have not identified a motive for Sunday’s attack inside one of Scandinavia’s biggest shopping centres.

The suspect, carrying a rifle and knife, was quickly arrested, and Copenhagen chief police inspector Søren Thomassen said the man also had access to another gun. He said the firearms were obtained illegally but gave no further details.

“It was the worst possible nightmare,” Danish Prime Minister Mette Frederiksen said on Monday, calling the attack “unusually brutal”.

The three killed were a 17-year-old boy and a 17-yearold girl, both Danes, and a 47-year-old Russian man, according to Thomassen. Four more people were hospitalised with gunshot wounds and were in critical but stable condition.

In all 30 people were hurt, most in the panicked stampede after the shots rang out at the Field’s shopping centre, on the outskirts of the Danish capital. Gun violence is relatively rare in Denmark. The last shooting on this scale was in February 2015, when a 22-yearold man was killed in a shootout with the police after an attack in the capital that left two people dead.

The suspect, who cannot be named by court order, was brought before a judge on Monday in a packed courtroom to face three preliminary charges of murder and four

of attempted murder. That’s a step short of formal charges but allows authorities to keep a person in custody during an investigation. The judge asked the media to leave and held the detention hearing behind closed doors. It wasn’t immediately clear how the suspect pleaded. He will remain in custody until July 28, police said.

Thomassen said the police had no indication that anyone helped the man. “There is nothing in our investigation, or the documents we have reviewed, or the things we have found, or the witnesses’ statements we have gotten, that can substantiate that this is an act of terrorism,” said Thomassen, who previously identified the man as an “ethnic Dane”, a phrase typically used to mean someone is white.

Danish broadcaster TV2 published a grainy photo of the alleged gunman, a man wearing knee-length shorts, a vest or sleeveless shirt, and holding what appeared to be a rifle in his right hand.

“He seemed very violent and angry,” eyewitness Mahdi Al-Wazni told TV2. “He spoke to me and said it (the rifle) isn’t real as I was filming him. He seemed very proud of what he was doing.” Images from the scene showed people running out of the mall, where people laid flowers on Monday.

Chassandra Stoltz, an 18-year-old student who was on her way to a concert that was scheduled for Sunday night nearby, described a stampede as the shots rang out. At first, she and her sister and father thought it was because someone had spotted Styles — but she soon realised the panic, including a man who grabbed his child from a stroller in the chaos.