The 46-year-old Lindh died at a hospital Thursday, a day after she was chased up an escalator and repeatedly stabbed in the stomach, chest and arm. Her attacker fled, dropping his knife and camouflage jacket.
Police said they were searching for a 6-foot Swedish man with bad skin and shoulder-length dark-blond hair, possibly with a criminal record. They said he was about 30, clean-shaven and wore a hooded sweater and hat when last seen. Borders and ferries were being monitored closely. No arrests have been made.
Swedish Prime Minister Goeran Persson said Sunday's referendum on adopting the euro — the common European Union currency backed by Lindh — would go ahead, though he ordered an immediate halt to campaigning.
Police do not believe the attack was politically motivated, despite the fact that it came just three days before the referendum vote.
"There is nothing that indicates there was any careful planning in this," Persson said of the attack.
Police spokesman Leif Jennekvist acknowledged police were in need of clues, but ruled out the possibility the suspect might evade justice, like the attacker who killed Prime Minister Olof Palme in 1986.
"We are going to find him," Jennekvist said. "That's our job."
The attack on Lindh raised concerns in Sweden and its Nordic neighbors about the openness of their countries, where it's common to see a prime minister jogging without bodyguards and politicians strolling the streets with their families.
Critics said Sweden's security agency, known as SAPO, should have learned more from the murder of Palme, who was shot in downtown Stockholm while walking with his wife. Like Lindh, Palme had no bodyguard.
"In the middle of all the grief, you almost feel some anger," said Jan Nygren, a former Cabinet minister. "How could this happen? And again?"
Although security was tightened after Palme's murder, only the prime minister and the king now are afforded round-the-clock protection. Other Cabinet ministers have them when security officials believe they're needed.
SAPO said Lindh had no bodyguards when she was attacked Wednesday because there had been no threats against her.
"Of course it feels like a failure when this kind of event happens involving a person that we have the responsibility to protect," acting SAPO chief Kurt Malmstroem said. "But whether we have made a mistake in evaluating information and other things, the future will tell."
He said security had been temporarily heightened around government officials, but declined to give details.
Jerzy Sarnecki, a Stockholm University criminology professor, criticized SAPO, noting Lindh was a leading figure in the Social Democratic government's efforts to persuade Swedes to adopt the euro in Sunday's referendum.
"To put it mildly, how the hell can you say that there wasn't a threat in a politically inflamed situation?" he said. "That's not the assessment I would have made."
Such criticism echoed across Stockholm on Thursday. Flags flew at half-staff throughout the country of 9 million, and in the Riksdag, or parliament, lawmakers held a moment of silence. Many churches were kept open for mourners.
"Our society has become tougher. There is so much violence now. We have to battle that more," said Hans-Olov Jordaas, 70, a former politician. He added that it was a "catastrophe" that police and the security services had not protected Lindh.
"That's absurd. What's the point, if you wait for a threat?" he asked.
Tributes poured in from around the world to Lindh, who many Swedes believed might have become prime minister.
In Washington, Secretary of State Colin Powell emotionally recalled his friendship with Lindh: "She had a special energy, integrity and compassion and she spent a great deal of her time focusing her efforts on global humanitarian issues. Anna was a cherished colleague and friend, and I will miss her.
Around Stockholm, posters bearing Lindh's image and pushing for a "yes" vote in the referendum were bedecked with red and white roses.
One such billboard was across the road from the site where Palme was murdered. The plaque marking the spot was encircled in carnations, roses and lilys, seemingly in concerted remembrance of Lindh, who was part of the same political party.
Persson called Lindh "a good representative" of Sweden's "openness" and "democratic society," and said the country should retain the closeness between citizens and elected officials.
But national police chief Sten Heckscher suggested that policy could be reviewed because of Lindh's slaying.
"My personal guess is that if one were to leave that (policy), it would be with a lot of reluctance," he said.
The slaying stunned Sweden's Nordic neighbors.
"It is an attack on our open form of democracy," Norwegian Prime Minister Kjell Magne Bondevik said. "We have to be more watchful, but I feel safe. ... If we close ourselves in, we will lose some of the openness of our Nordic societies."
Bondevik said his government began examining its security procedures after learning of Lindh's stabbing.
In Finland, Prime Minister Matti Vanhanen described the attack as "a major setback and shock" to the open societies of the Nordic countries.