AMSTERDAM – Thousands of people, including the Dutch prime minister, gathered Sunday evening to lay flowers and mourn at a candlelit memorial service outside a mall in a quiet Amsterdam suburb where a mentally troubled young man shot six people dead a day earlier.
Investigators are still puzzling over the gunman's motive and trying to understand how he was able to obtain and legally own five firearms in the Netherlands, where gun control laws are considered strict, despite prior run-ins with the law and a stay at a psychiatric institution.
The attacker, identified as 24-year-old Tristan van der Vlis, opened fire at the Ridderhof mall in Alphen aan den Rijn with an automatic rifle on one of the first pleasant Saturdays of spring, authorities said. Many of his fatal victims were elderly people unable to flee.
At the ceremony, Mayor Bas Eenhoorn asked for special attention for those he called the "heroes of the Ridderhof" — people who tried to help others escape the shooting including one, not named, who was among those killed as a result. Prime Minister Mark Rutte summarized the attack as an "incomprehensible deed and a terrible day" in Dutch history.
In addition to those killed, the gunman wounded at least 17 people, including two children, and dozens more suffered minor injuries, including one infant. Van der Vlis ended the rampage by shooting himself fatally in the head, bringing the death toll to seven.
At a news conference Sunday, District Attorney Kitty Nooy said the investigation had uncovered notes left by the killer and more information in several files on his computer.
"What I can say about that is the broad lines, and this is, of course, very sad for the victims' families, but that no clear motive can be found there," she said. "This man was clearly suicidal, and the contents are more of a spiritual than a threatening nature."
Twelve people remained in hospital, Eenhoorn told reporters. The children with serious injuries were both girls, aged 10 and six, one of whom has since been released from hospital.
Authorities did not publicly release victims' identities, citing privacy reasons. Eenhoorn said the victims all lived in Alphen, but one was an 42-year-old immigrant from Syria, a poet.
"And it was in our 'safe' country that he died because of this violence," Eenhoorn said.
Alphen is about 20 miles (30 kilometers) southwest of Amsterdam.
Van der Vlis' apartment building remained under police guard. Neighbors gave mixed comments about his character.
"He seemed to me to be a nice guy, he always greeted me nicely," said Veronique Troon. But she said that one time he asked her about her native Brazil, saying: "'that seems like a very, very dangerous country, don't you think so?' I found it very weird."
An online condolence register has been signed more than 9,000 times.
"It's unbelievable. I thought such things could happen only in America, but it's here too," said Gisele Klaas, attending the memorial. "I'm not afraid of the future, but I hope such a thing never happens again."
Witnesses, including some interviewed by The Associated Press, said the blond-haired gunman wore camouflage trousers and a black jacket as he stalked through the mall, shooting people at random. The attack lasted around 10 minutes, and witnesses saw him changing magazines in his gun.
The exact type of weapons he used have not been made known, but the city as confirmed he had permits for five, and he had three with him at the time of the attack, one of which was an "automatic weapon."
Witnesses said he later shot himself in the head with a revolver.
Nooy said an investigation about whether Van der Vlis had properly been granted gun permits has been given to prosecutors from a different jurisdiction to avoid any conflict of interest. She said that a 2003 run-in Van der Vlis had with police over a weapons possession charge — when he would have been a minor — had turned out to involve an air rifle.
But no explanation was offered for how he could have been granted any permit after having spent 10 days in a psychiatric institution in 2006 because he was so depressed health workers were concerned he might commit suicide.
Van der Vlis lived with his father in an apartment near the mall and both parents were said to be cooperating with the investigation.
"It appears that he stopped working for a staffing company several weeks ago," prosecutors said in a statement. "He was down, but it was not known that he was suicidal. His actions yesterday came as a total surprise."
Under Dutch law, owning revolvers and rifles is only allowed with a license, and they must be kept unloaded and locked unless they are in use at a firing range or during hunting. In theory, only the military and special police forces have access to fully automatic firearms.
However, despite their illegal status, automatic weapons are frequently found during drugs busts and used in gangland killings.
Nooy said she was still unable to say whether Van der Vlis had permits for the guns he actually used in the attack, but added "it appears that it's reasonably easy to convert one of the weapons" from semiautomatic to fully automatic.
Saturday's violence is unusual in the Netherlands, but not unprecedented.
In the past 15 years the country has had two school shootings, one political killing and one terrorist attack — the 2004 murder of filmmaker Theo van Gogh by an Islamic fanatic, which was followed by a standoff with militants armed with machine guns and hand grenades. In 2009, a man killed eight people and wounded 10 by driving his car through a crowd watching a royal parade.