A sign is laid Monday in London to mourn the victims of the Paris terror attacks. Getty Images

Turkey warned France about the threat posed by suspected Paris killer Omar Ismail Mostefai at least twice before the Friday night attacks, a Turkish official told the Guardian. French authorities did not respond with an information request regarding Mostefai until after the coordinated attacks that killed at least 129 people.

Mostefai was identified Saturday evening alongside an "Abbdulakbak B." as two of the eight individuals who took part in the shootings and bombings across Paris Friday that have been claimed by the Islamic State militant group, also known as ISIS. Other attackers have been identified as Samy Amimour and Ahmad Al Mohammad, who was a Syrian passport holder. There were 352 individuals wounded in the turmoil, and at least 99 of those people were in critical condition.

French President François Hollande told the country that Friday’s series of incidents was “an act of war that was committed by a terrorist army, a jihadist army, Daesh, against France.” Daesh is an acronym for ISIS' full Arabic name.

The fact that Al Mohammad possessed a Syrian passport quickly brought forth concern over the refugee crisis that has brought nearly a million people into Europe since the Syrian Civil War began in March 2011. European countries reacted with concern, and news outlets reported that the Paris attackers “sneaked into Europe as fake Syrian refugees.”

The mastermind of the attacks has been identified as Abdelhamid Abaaoud, a Belgian national who is believed to be fighting in Syria with ISIS. Abaaoud is a 27-year-old who grew up in a Brussels suburb.

Paris was thrust into turmoil and confusion Friday evening just after 9 p.m. when armed teams drove by cafes and opened fire. Near the Stade de France, where the French national soccer team was playing Germany, three explosions occurred. Later, gunmen entered a concert at the Bataclan, where an American band was playing, and began slaughtering the crowd.