Shocked by Friday's attack that left four dead and 15 injured -- for which a 39-year-old Uzbek man is in custody -- Stockholmers mobilised on Facebook, organising a vigil for 2pm at the Sergels Torg plaza near where the truck rammed into shoppers.
Sweden has been trying to get back on its feet this weekend after what authorities termed a terror attack, the motive for which was still unknown.
There has been no immediate claim of responsibility for the Stockholm attack -- the third in Europe in two weeks, coming on the heels of the car and knife assault outside London's parliament and the Saint Petersburg metro bombing.
Police have not named the suspected driver of the truck, whom they arrested on Friday evening, but authorities said he was known to Sweden's intelligence service for undisclosed reasons.
The man is suspected of speeding a stolen beer truck several hundred metres down the bustling pedestrian street Drottninggatan in the heart of Stockholm.
The vehicle mowed down shoppers before slamming into the facade of the busy Ahlens department store.
"There is nothing to indicate that we've got the wrong man. On the contrary, the suspicions have strengthened," Swedish police chief Dan Eliasson said Saturday.
He said police found a suspect device in the cab of the truck.
"A technical examination is ongoing, we can't go into what it is right now... whether it's a bomb or a flammable device."
The attack deeply shocked the usually tranquil Scandinavian nation, which prides itself on its openness and tolerance.
All day Saturday, crowds milled behind the security fences blocking off the scene of the attack, laying flowers on the ground or poking them into the fence.
Several police cars parked near the scene were also covered in flowers by Swedes, who widely praised the emergency crews' speedy response to the attack.
"Maybe something good will come of this," Inger Morstedt, 75, told AFP, expressing hope that her fellow Swedes would become "even more open and welcoming".
"In some ways it's unreal," said 40-year-old Johan.
"I've come here to honour the victims and the society in which we live."
Flags flew at half-mast at public buildings across Stockholm on Saturday.
Prime Minister Stefan Löfven, who beefed up border controls on Friday after the attack, announced a national minute of silence to be held in honour of the victims on Monday at noon.
"Today, all of Sweden is in mourning, but we're going to get through this together," he told reporters on Saturday after laying a bouquet outside the Ahlens department store.
King Carl Gustaf XVI, who returned to Stockholm on Saturday after cutting short a visit to Brazil, also addressed the nation outside the palace.
"The consideration people are showing each other shows the strength of our society," he said.
"There are so many of us who want to help, many more than those who want to hurt us."
Friday's attack was the second terror attack in Stockholm.
In December 2010, a suicide bomber blew himself up, also on the Drottninggatan street, lightly injuring several passers by.