The best reason the EU bank should file a SAR/STR is that the events raise concerns that the payment represents proceeds from insider trading, which is a form of market abuse and a predicate offense for money laundering in many jurisdictions. The fact that the originator was indicted by U.S. law enforcement, arrested in Switzerland, and extradited for alleged insider trading indicates that there is a strong suspicion that the funds are derived from criminal activity. The other options are not sufficient reasons to file a SAR/STR, as they do not directly relate to the nature or source of the funds.

References: [Financial Action Task Force Report on Money Laundering and Terrorist Financing Risks and Vulnerabilities Associated with Gold], page 17 : [Leading Complex Investigations Certificate], page 12