COPENHAGEN, Denmark (AP) — The Danish gunman who attacked a free-speech seminar and a synagogue in Copenhagen was released about two weeks ago from a jail where he may have been radicalized while serving time for a vicious stabbing.

As Denmark mourned the two victims, these and other troubling details emerged Monday about Omar Abdel Hamid El-Hussein's path to the country's worst terror spree in three decades.

El-Hussein was arrested 15 months ago in a vicious knife attack on a train passenger, and while he was awaiting trial, a change in his behavior last summer set off enough "alarm bells" for jail authorities to alert PET, Denmark's counter-terror agency, a source close to the investigation told AP.

Such warnings usually set in motion counter-radicalization efforts, such as counseling in jail. It wasn't immediately clear how aware the court was of this issue before El-Hussein was convicted of a lesser charge.

Sentenced to the time he had already served, he was released about two weeks ago, the source said, speaking on condition of anonymity because police haven't officially identified the gunman.

"We are working on finding out what has happened," PET spokeswoman Lotte Holmstrup said Monday.

The agency's director, Jens Madsen, also wouldn't elaborate, but he confirmed Sunday that the agency had been aware of the gunman, and that El-Hussein may have been inspired by last month's attacks by Islamic extremists in Paris that killed 17 people.

The 22-year-old opened fire at a cultural center and a synagogue — targets that resembled the Paris attackers' rampage at the Charlie Hebdo newspaper and a Jewish grocery store — before he was killed in a gun battle with a SWAT team early Sunday. His victims included a Danish documentary filmmaker and a Jewish security guard; five police officers were wounded.

Denmark's prime minister and crown prince and foreign dignitaries joined about 30,000 people honoring the victims in the bitter Monday evening cold outside the Krudttoenden cultural center, whose name in Danish translates to "powder keg."

"I am here with my daughter to show her that we live in a free country. No one must ruin it," said Aisha Abdi, a Somali Muslim and political refugee who brought her 12-year-old daughter, Irina.

Also Monday, a judge ordered 10 days of pre-trial detention for two people accused of helping el-Hussein get rid of a weapon while evading authorities. Both men deny the charges, said Michael Juul Eriksen, a defense lawyer for one of the two.

Many Danes first saw el-Hussein's image in November 2013, when he was wanted by police for gravely wounding a 19-year-old student in his left thigh and buttocks with a large knife.

El-Hussein didn't come across as religious, and had the appearance of a "hardened criminal," his shaved head pocked by scars, said Jesper Braarud Larsen, a Danish court reporter who covered his trial in December.

Surveillance video of the commuter train attack was so vicious that the victim's sobbing parents had to leave the courtroom, but El-Hussein didn't even flinch, Larsen recalled.

El-Hussein told the court he had smoked hashish and was feeling paranoid when he randomly attacked the student. Prosecutors charged El-Hussein with attempted homicide but a judge convicted him of aggravated assault, taking into account El-Hussein's claim that he never meant to kill the victim, said Larsen, who works for the Danish news site Dagens.dk.

El-Hussein's defense lawyer from that case didn't return calls seeking comment, and court documents weren't immediately available to corroborate the account.

Denmark has foiled a series of terror plots since the 2005 publication of 12 caricatures of the Prophet Muhammad in the Jyllands-Posten newspaper triggered riots in Muslim countries and calls for vengeance.

Swedish artist Lars Vilks, who caricatured the prophet in 2007, was at Saturday's free speech event. Whisked away unharmed by his bodyguards, Vilks told the AP he thought he was the intended target.

Other participants dropped to the floor, scrambling for somewhere to hide as the gunman sprayed bullets through the glass windows and then fled. Later Saturday, he visited an Internet cafe before moving on to the synagogue.

Police raided the cafe on Sunday and detained four people, including the two men arraigned on Monday. The other two were released. "We are of course interested in whether he was alone and whether he was carrying anything and in which direction he went," police spokesman Joergen Skov said.

While mourners placed hundreds of flower bouquets and candles at both shooting scenes, a smaller mound of flowers appeared where the gunman was slain. Ozlem Cekic, lawmaker of the left-wing Socialist People's Party, called that another "huge assault on the Danish population." Later in the day, a group of young men removed the bouquets, telling Denmark's TV2 network it isn't a Muslim tradition to honor the dead with flowers. They shouted "God, is great" in Arabic.

The shooting spree was Denmark's worst terror attack since a bomb exploded outside the Copenhagen office of the North West Orient airline in 1985, killing a 27-year-old Algerian tourist.

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AP journalists Jan M. Olsen and Philipp-Moritz Jenne in Copenhagen contributed to this report.