No motive has been uncovered so far in a shooting, which saw three people killed at a shopping centre in Copenhagen.
Three others are in a critical condition after the shooting in the Danish capital on Sunday.
A 22-year-old Danish man was arrested after the shooting at the Field's Shopping Centre, one of the largest in Scandinavia, Copenhagen chief inspector Soeren Thomassen said.
He said the victims included a man in his 40s and "two young people," without giving further details.
Several others were injured, three critically, he added.
Nikolaj Skydsgaard, a Reuters reporter based in Copenhagen, told Newstalk Breakfast police are still looking for any motive.
"We know now that there was no particular motive from this 22-year-old man.
"Police haven't been able to uncover anything in terms of race or gender or anything - the victims of this attack were random.
"Among those critically wounded are two Swedish citizens, and one of the three killed was a Russian man who was residing in Denmark".
He says it is still unclear whether this was a terrorist incident.
"Yesterday they weren't able to rule out whether this was an act of terror.
"But they have nothing today, after an intense night of investigation, to support that this was an act of terror now".
The man arrested is due in court later.
"He's going to be put in front of a judge later today, and he's going to be charged with manslaughter for now", Nikolaj adds.
Chief inspector Thomassen said police first received reports of a shooting at 5.37pm on Sunday and arrested the suspect 11 minutes later.
He said there was no evidence that the perpetrator was working in conspiracy with others.
Footage shows the alleged gunman wearing knee-length socks, a vest or sleeveless shirt, and holding what appeared to be a rifle.
Images from the scene showed people running from the shopping centre.
"People first thought it was a thief... Then I suddenly hear shots and threw myself behind the counter inside the store," eyewitness Rikke Levandovski told broadcaster TV2.
"He is just shooting into the crowd, not up in the ceiling or into the floor," she added.
Another witness, who gave her name as Isabella, told public broadcaster DR: "My friend and I... suddenly we hear shots. I hear about 10 shots and then run as fast as we can into a toilet.
"We squeeze into this tiny toilet where we are around 11 people."
Danish Prime Minister Mette Frederiksen said the country had been hit by a "cruel attack".
"It is incomprehensible. Heartbreaking. Pointless," she said. "Our beautiful and usually so safe capital was changed in a split second."
Taoiseach Micheál Martin said he was "shocked and saddened by the events in Copenhagen."
"My deepest sympathies to the families and friends of those killed and injured. Thoughts are with the people of Denmark", he tweeted.
It was the worst gun attack in Denmark since February 2015, when a 22-year-old man was killed in a shootout with police after going on a shooting rampage in the capital - which left two people dead and five police officers wounded.
Additional reporting: IRN