Earlier quoted context omitted.
Judging from TFA none of this was determined. They (allegedly) matched the length of the encrypted name using a process of elimination from an AI-generated pool of possible names, arriving at one name that happened to match the name of Elizabeth Short's murderer, and then a bunch of other circumstantial details aligned.
In the article it also says the key to deicpher was Elizabeth and that the solution was approved by two cryptographers at the NSA
Huh, apparently I didn't read the whole thing then.