When a policewoman was gunned down the next day, police first thought the incident was unrelated.
But when that gunman, Amedy Coulibaly, took hostages at a kosher supermarket the next day, demanding that police stand down from a siege of the Kouachi brothers happening just outside the city, a web of connections started to become clear.
And as investigators look into the horrific events that shook France and the world this month, it becomes clear that the links spread from Paris out to Yemen, Syria, Iraq and beyond.
A week after the Charlie Hebdo killings, al Qaeda's Yemen affiliate, al Qaeda in the Arabian Peninsula, said that it had planned and funded the attack years earlier. In a video message, AQAP credited the American-born radical preacher Anwar al-Awlaki
with giving the orders before he was killed in 2011.
Separately, a video emerged that appeared to show Coulibaly pledging allegiance to the leader of another terror group, Abu Bakr al-Baghdadi, the self-proclaimed caliph of the Islamic State in Iraq and Syria
Through legal papers, jihadi websites, press reports and its own investigations, CNN has pieced together other connections.
When they were in their 20s, the Kouachi brothers were part of a circle of Parisian Islamists inspired by Farid Beyettoun, police allege in court papers seen by CNN.
Later, Cherif Kouachi was in jail with Djamel Beghal, who was accused of being a top al Qaeda recruiter. Coulibaly and his wife, Hayat Boumeddiene, often visited Beghal when he got out of prison, as did Kouachi.
Both Kouachi brothers and Coulibaly are dead, but Boumeddiene is on the run, and investigators are continuing to look into who knows whom, and what the connections could reveal.