[Who are half these people though, she focuses on last names for most of them...]

From that list, anyone who spoke with him is suspect. The fact that he is a yakuza heir would not be enough to deem him a threat this early. He would be a better target for conversion, if one were only looking at his profile.

Thus, someone had to know that he would never allow himself to be converted.

Thus, it was someone with whom he spoke. Do you follow?