Assassination was a skilled job, especially the assassination of a heavily protected dignitary, a head of state.
Sometimes a bullet could solve a lot of problems. However, it would also bring about more problems that were no less than the problems it solved.
Ghost Agents would wear the optical invisibility gear. Then, fire a few bullets… Definitely wouldn't work.
Not to mention the exposure of optical invisibility would cause the security departments of all countries to add infrared and acoustic wave sensing devices. Optical invisibility was just invisible to the naked eye and not a true-sense of disappearance. If the Ghost Agents really used brute force for this assassination under everyone's watch, Carmen would laugh even in his dreams.
There was no need to investigate who mastered optical invisibility technology. Even if NATO didn't form a consensus in its organization, they would be forced to make a move.
