Unmixing the mix: Patterns and challenges in Bitcoin mixer investigations

This paper investigates the operational patterns and forensic traceability of Bitcoin mixing services, which pose significant challenges to anti-money laundering efforts. We analyze blockchain data using Neo4j to identify unique mixing patterns and potential deanonymization techniques. Our research includes a comprehensive survey of 20 currently available mixing services, examining their features such as input/output address policies, delay options, and security measures. We also analyze three legal cases from the U.S. involving Bitcoin mixers to understand investigative techniques used by law enforcement. We conduct two test transactions and use graph analysis to identify distinct transaction patterns associated with specific mixers, including peeling chains and multi-input transactions. We simulate scenarios where investigators have partial knowledge about transactions, demonstrating how this information can be leveraged to trace funds through mixers. Our findings reveal that while mixers significantly obfuscate transaction trails, certain patterns and behaviors can still be exploited for forensic analysis. We examine current investigative approaches for identifying users and operators of mixing services, primarily focusing on methods that associate addresses with entities and utilize off-chain attacks. Additionally, we discuss the limitations of our approach and propose potential improvements that can aid investigators in applying effective techniques. This research contributes to the growing field of cryptocurrency forensics by providing a comprehensive analysis of mixer operations and investigative techniques. Our insights can assist law enforcement agencies in developing more effective strategies to tackle the challenges posed by Bitcoin mixers in cybercrime investigations.