Only a detailed investigation can uncover what vital clues may have been missed as to the extremist leanings and murderous intentions of the killers.
These are some of the questions that need answers.
What happened to the tracking of the killers by the police and security agencies?
Two were known to the authorities. It is also believed that there were links with extremists in the UK and Yemen.
It is reported that the police decided to stop tracking them six months earlier.
What were the reasons behind this decision?
Were vital clues lost when it came to sharing information between the French authorities and other international agencies?
How organised were the attacks? What was the precise level of co-ordination and planning?
Was it a "home grown" terror attack, with inspiration and training coming from elsewhere?
Or was it planned and instigated through a wider network?
The claims of the perpetrators themselves have to be treated with caution until more is known about the detailed planning of the attacks and the training and travel movements of the individual terrorists.
How and where did the killers obtain the weapons to carry out the attacks?
How did they manage to conceal their arms cache without someone becoming suspicious?
Are there others still at large who may have helped?
The acquisition and transport of the weapons seems to have slipped past the radar of the police.
What role did Hayat Boumeddiene play?
The Turkish foreign minister said the widow of the Jihadist in the deli siege flew to Turkey on 2 January, well before the Charlie Hebdo massacre. She is now said to be in Syria.
We simply don't know enough about her role at this stage but some reports say she helped plan the attacks.
Pictures have emerged in recent days appearing to show her engaged in terror training.
Why is so much of France's Muslim population behind bars?
No official figures exist because there appears to be no formal monitoring of numbers.
But some reports have spoken of around 70% of the prison population being made up of Muslims.
It is known that French prisons are a major source of radicalisation, so what are the authorities doing to combat that?
In the days and weeks ahead, the French police and intelligence agencies will be picking through every aspect of the terror attacks in Paris.