In a recent Fourth Circuit opinion, the court analyzed 404(b) evidence vs. res gestae. Essentially, the rules of evidence prohibit evidence of a prior bad act to prove that that person acted in conformity with those prior acts (e.g., he did something bad before so it is likely he did the bad act which he is currently accused of). However, 404(b) has exceptions such as motive, intent, ID, etc.
There is another exception to 404(b) that is called res gestae ("things done"). This type of intrinsic evidence is not considered prior acts because it is part of the whole picture. It is used to explain a continuing situation. So the question that comes up: when did the "situation" start and when did it end?
In this case, the court said:
The court allowed in the prior act evidence because it involved "the same series of transactions as the charged offense."
United States v. Sutherland, 921 F.3d 421 (4th Cir. 2019)