Bitcoin tracking follows UTXOs from the transaction that created them to the later inputs that spend them, then layers wallet and service attribution onto that public graph.
Inputs reference prior outputs
Every ordinary input names a prior transaction ID and output index. That spending relationship is explicit and cannot be changed without invalidating the transaction.
Transactions create new branches
Payments, change, and multiple recipients become new outputs. Analysts observe when each is spent and may estimate which outputs share control.
Where heuristics enter
Common-input ownership and change detection can be useful but are not universal proof. Collaborative transactions and wallet behavior can complicate them.
Off-chain attribution
Exchange records, public addresses, merchant invoices, and user disclosures can connect graph nodes to entities. The chain itself usually contains addresses rather than legal names.
How to read the evidence
Bitcoin analysis should follow actual UTXOs rather than an account-style balance narrative. Record which outputs were selected as inputs, which new outputs were created, how fees changed the total, and what later transactions spent those outputs. Change and common ownership may require heuristics, while the input-to-output references are explicit. A cross-asset route begins after those public Bitcoin facts already exist.