From the moment he encountered Kaspar, Roland had actually given up on the idea of disrupting the Empire's entire plan by preventing the terrorist attack.
Not to mention facing the formidable military force of Lutèce, where even the Schutzstaffel had been mobilized and the Emperor himself might arrive, just how feasible was the success of the struggling "Freedom Legion" within Lutèce City? The mere point that they couldn't confirm whether all the spies in the Lutèce branch had been completely eradicated was enough to make Roland abandon the original action plan.
What kind of enormous nerve and strong heart does it take to forcefully execute a leaked operation plan when you know you are being monitored?
Since military intervention was no longer viable, seeking an alternative path around the impenetrable defenses of the Empire became the only choice.