My point wasn't when the 10 commandments were allegedly handed down, mostly because I don't believe they ever were the word of a God/Deity or other entity non human, any more than I believe some aquatic tart slung a sword to King Arthur.
The point is that however they were arrived at, the concept was adopted by Christianity, and are the basis of much of common law, along with many other Christian beliefs. So is a valid answer to the question about what laws are based on Christianity.
An eye for an eye, another apparently Christian concept, isn't justice when it happens without due process. Even IS have a pretend trial. But while I see your point and part of me agrees, it wouldn't help, the mindset is that they have done something 'glorious' and for their 'God', because it is 'his will'. Killing them wont deter or punish, and in reality will simply be used to egg more of the same on by confirming in their minds the idea of martyrdom.
Treating terrorists like criminals is a better way, France doesn't have a death sentence, so life, meaning life is a far better way of dealing with it.