COPENHAGEN, Denmark (AP) — 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 Monday, all but ruling out that the attack was related to 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.

After the custody hearing, defense lawyer Luise Høj said she agreed to have her client undergo a mental exam. She did not comment on the charges. Police have said the man was known to mental health service without elaborating.

Police have not identified a motive for Sunday’s attack inside one of Scandinavia’s biggest shopping centers. 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 Monday, calling the attack “unusually brutal.”

The three killed were a 17-year-old boy and a 17-year-old 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, around two dozen people were hurt, most in the panicked stampede after the shots rang out at the Field’s shopping center, 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-year-old man was killed in a shootout with police after an attack in the capital that left two people dead and five police officers wounded.

The suspect, who cannot be named by court order, was brought before a judge 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 allow authorities to keep a person in custody during an investigation.

It wasn’t immediately clear how the suspect pleaded. He will remain in custody until July 28, police said.