A two-digit number (i. e. "13") would be too short for the redaction. A three- or four-digit number is highly unlikely ( because it would be treated as a single conspiracy, not as separate investigations of individuals). Plus, the sentence that follows after the colon seems to be a list of the individuals, and its length points at a single-digit number.
maybe there's some standard style guide that rules that out?
I would be interested in seeing how many "matches" digits would yield
I don't know if it's an official style somewhere or not, but I was always taught 1-9 you spell out (one, two, three,...) And 10+ you write digits (10, 11, 12, 13,...). With a few exceptions, like if two numbers are next to each other.