Here's How Berlin Is Different From Other Recent Attacks

The attack at a market in Berlin, Germany, where a man drove a truck into a crowd of shoppers, left at least 12 people dead and 50 people injured on Monday. Unlike some other recent attacks, the initial suspect has been let go due to a lack of evidence. 

German Chancellor Angela Merkel called it a probable "terror attack," the suspect striking on one of the busiest nights in the lead up to Christmas.

The Islamic State has claimed responsibility for the attack, saying the driver was one of its "soldiers."

Authorities had one suspect in custody, a Pakistani asylum seeker, who denied any involvement, according to The Washington Post. Officials released him on Tuesday because of a lack of evidence, and no suspect sketches or photos have been released to the public so far.

"We have to entertain the theory that the detainee might possibly not have been the perpetrator," said prosecutor Peter Frank, the BBC reported.

The truck used in the attack had departed Poland to deliver a load full of steel, but the original driver was found shot dead in the passenger seat after the attack, according to the Post. 

The Berlin attack has drawn comparisons to the Nice truck attack. 

BREAKING: At least 77 people killed in truck attack in Nice, France.

Posted by ATTN: on Thursday, July 14, 2016

In July, Mohamed Lahouaiej Bouhel slammed a truck into French families and tourists in Nice, France during a national holiday, killing 85 people. He was shot dead at the scene by law enforcement. Within two days of the attack, the Islamic State claimed responsibility, calling Bouhel a "soldier." 

The U.S. State Department has warned about the threat of attacks this holiday season. 

Travel alert for Americans abroad.

In November, the U.S. Department of State issued a travel warning for Americans going abroad to Europe during the holidays. The State Department warned about "credible information" that the Islamic State and its supporters were planning an attack in Europe around holiday events. 

"Credible information indicates the Islamic State of Iraq and the Levant (ISIL or Da'esh), al-Qa'ida, and their affiliates continue to plan terrorist attacks in Europe, with a focus on the upcoming holiday season and associated events," reads the warning. "U.S. citizens should also be alert to the possibility that extremist sympathizers or self-radicalized extremists may conduct attacks during this period with little or no warning."

U.S. officials previously warned about the potential for vehicles being used as terror weapons.  

In 2010, the FBI and the Department of Homeland Security issued a warning about the potential for terrorists to use cars and trucks to kill.

"Terrorist Use of Vehicle Ramming Tactics."

However, a mass killing in the U.S. is still far more likely to be carried out with a gun. 

ATTN: talked to terror expert and senior fellow at the Foundation for Defense of Democracies Daveed Gartenstein-Ross, Ph.D. after the Nice, France truck attack in July. He noted that "mass tragedies" in the U.S. are almost always carried out with firearms.

"The kind of attacks that we have in the United States where people get killed, they're primarily shooting attacks," he said. "It's based off of the likelihood that if a mass tragedy hits your community, where a number of people are killed by someone intentionally targeting them, just by sheer percentages it's likely to be shooting."

RELATED: The FBI Gave a Grim Warning About the Attack in Nice, France 6 Years Ago