It was the mistake of our Security Agencies that these kind of people can go out easily and also able to run their business from outside country. It was also limitation to the Govt. otherwise it would be further dificult to get the culpit.
If, death sentence is given and Govt. wants, They have many ways and means to execute him.
It will depend on the GOVT. on how to use the Power. It's our Coutries look-out. And I am sure the FRANCE will also give permission, If prooved with proper documents.