Twelve people were killed and dozens more were injured after a large truck plowed into a Christmas market in Berlin. The Islamic State has claimed responsibility for the attack. (Victoria Walker,Peter Stevenson/The Washington Post)

A truck plowed through a bustling Christmas market in Berlin on Monday evening, killing 12 people and wounding 48 people. Here's what we know so far:

Monday, Dec. 19

The Breitscheidplatz square in Berlin hosts one of the city's most famous Christmas markets. On the evening of the attack, visitors to the market were drinking mulled wine and enjoying the sights and the sounds.

Shortly after 8 p.m. local time, there was a loud noise, according to witness accounts.

“We heard a loud bang,” Emma Rushton told CNN. “And we started to see to our left Christmas lights were being torn down.” Rushton said she saw a truck driving into the crowd.

The truck veered onto the sidewalk and crashed among market stalls. It traveled 50 to 80 feet before coming to a stop.

Some victims were pinned under the truck's wheels. Others were struck and tossed onto the pavement.

Jan Hollitzer, deputy editor in chief of Berliner Morgenpost, told the BBC that he saw people lying on the ground and under the truck.

First responders carried people away on stretchers as police with automatic weapons cordoned off the area.

Police said two men were inside the truck. One, who was found dead, was a Polish national. German police used social media to ask people to stay at home and “spread no rumors.”

Social media users worldwide took to Facebook and Twitter to express solidarity with the people of Germany, using the hashtag #PrayForBerlin.

A Pakistani asylum seeker was detained in the attack, which German Chancellor Angela Merkel called a likely “act of terrorism.” Police released the suspect Tuesday, citing a lack of evidence.

On Tuesday, the Islamic State claimed responsibility for inspiring the attack, calling the attacker a “soldier” responding to its call to target nations fighting the group in Iraq and Syria.

Flags are being flown at half-staff across Germany. Some Christmas markets remain closed.

Berlin's Brandenburg Gate was lighted up black, red and gold in memory of those who died in the attack.

Wednesday, Dec. 21

The capital remains on high alert.

German police are seeking a Tunisian asylum-seeker in the deadly Christmas market attack, according to law enforcement officials.

The man's asylum papers were discovered in the cabin of the truck used to ram the Christmas marketgoers.

Police are offering a 100,000 euro reward (about $100,000) for information leading to the capture of 24-year-old Anis Amri.

The attack in Berlin has lead some to scrutinize Germany's refugee policy, while others took to the streets Wednesday evening, chanting “refugees are welcome here.”

Floral tributes continue to grow at the site of the holiday market attack.