Accomplices, Aiding and Abetting, and the Like: An Overview of 18 U.S.C. § 2 [Updated February 14, 2020] [open pdf - 940KB]
From the Introduction: "Virtually every federal criminal statute has a hidden feature; helpers and hands-on offenders face the same punishment. This is the work of 18 U.S.C. § 2, which treats hands-on offenders and their accomplices (aiders and abettors) alike. This accomplice liability is much like that which accompanies conspiracy, and the rationale is the same for both: society fears the crimes of several more than the crimes of one. Aiding and abetting, unlike conspiracy, is not a separate crime; instead it serves as an alternative means of incurring criminal liability for the underlying offense."
CRS Report for Congress, R43769
Congressional Research Service: https://crsreports.congress.gov/