I guess ultimately it does come down to legal questions but reading some of the cases against them such as this [0] it doesn't seem like there's no ammunition for prosecutors to use. For example on pages (using page numbers listed at the bottom of the page) 104-105 that the Sacklers knew of several doctors that were suspected of prescribing opioids inappropriately yet continued to sell to them. Another example on page 112 states that Sacklers knew that they were selling to an illegal pill mill yet neither stopped selling to them nor reported it for 2 years. I note that other directors and executives are also named as defendants in this case. It most certainly doesn't seem that the Sacklers weren't involved in operations of Perdue, maybe not at a day to day level but they certainly were reported to and advised by Perdue staff very regularly (and they demanded plenty from the staff too).

[0]: https://www.mass.gov/files/documents/2019/01/31/Massachusett...