In the second memo — properly an addendum, not “supplemental” (apologies) — important to note that this is referring to a criminal investigation that would appear to be ongoing and conducted by an entity other than Mueller’s office. pic.twitter.com/KCPvLEgEPe

— Chris Geidner (@chrisgeidner) December 5, 2018

Geidner notes an important detail - Mueller notes that there are other active investigations ongoing outside the SCO. In other words, we may be seeing a reference to federal cases in EDVA, SDNY, or to possible investigations by the NY AG or others.