You're both right. It was Frank Jr. who wrote the letter to the Feds in 1998 or 1999 that started the whole ball rolling. Then, Nick flipped later.
Why did Frank Jr. write the letter?
Answer: He had stolen about $600,000 Dollars from his father's stash of cash. He didn't want to face his father so it was easier for him to keep him in jail. Frank Jr. was a drug user so he had that lying manipulating addict personality.
That was the bottom line for the reason Frank Jr. wrote the letter.
I have no idea of his drug usage presently. But, once an addict etc....