PARIS -- The search for the suspected assassins who opened fire on a satirical magazine continues as residents in France gather to mourn their loss in what is being called the worst terror attack in Paris in decades.
The City of Lights dimmed the bulbs on the iconic Eiffel Tower Thursday night. Paris is in mourning after 12 people were killed in a stunning act of terrorism.
The violence took place at the offices of the satirical paper Charlie Hebdo, which had been attacked in the past for publishing cartoons of the Muslim prophet Mohammad
.
At the Cathedral of Notre Dame, and all around France, people gathered with the message: "We are not afraid."
PHOTOS: 12 dead in terrorist attack in Paris
They stood together in solidarity against the attacks intended to strike fear into commentators, comedians, and cartoonists that would dare take on radical Islam.
"Wherever you are in the world, this is a tragic event," said one resident. "And I go to march on Saturday to show my defiance to murderers and evil fundamentalists."
The search for the suspected killers continues. One suspect turned himself in, but brothers Said Kouachi and Cherif Kouachi are still on the loose after allegedly opening fire in the paper's offices, killing 10 journalists and two police officers.
Tap to see video if viewing on News app.
One man in Northern France says police are going door-to-door, checking every house after two men resembling the suspects robbed a gas station there.
Officials say the brothers have possible ties to a Yemeni terrorist network. One of the men, Cherif, was convicted of terrorism in 2008. He served 18 months in prison for recruiting militants to fight the U.S. in Iraq.
His lawyer confirms that police tracked down the identities of the brothers because one of them left his ID behind in a getaway car.
And in the U.S., several places are now on heightened alert. A senior U.S. counterterrorism official says the two brothers were on the U.S. no-fly list.
Political satirists say they are not backing down.
"Cartoonists, if they're provoked not to do something, we'll do it," cartoonist Sam Gross said.
A message of defiance sent with a pen.
VIDEO: Bay Area cartoonist not surprised by Paris attack
To underscore that point, the remaining staff of the paper says that they will publish 1 million copies this week on time, which is a 3,000 percent increase of what they normally do. They are not backing down. And Google is donating #300,000 to help Charlie Hebdo publish its next edition.
On Thursday, President Barack Obama returned to Washington to pay his respects at the French Embassy.
A solemn-looking Obama wrote several lines in a condolence book set up on a spare table draped with a blue tablecloth.
The White House did not immediately comment on Obama's message to America's oldest ally.
Afterward, he stood briefly near the table with his head bowed before shaking hands with embassy personnel.
Obama has denounced the "cowardly, evil attacks" that took place Wednesday at the offices of the satirical newspaper Charlie Hebdo. He said the assault was an attack on journalists and a free press.
For the latest on the Paris terror attack, click here.
ABC7 News and The Associated Press contributed to this report.