Bgent: A Multi-Task Blockchain Investigation Agent with Executable Claim Checks

Blockchain investigations connect transaction execution, account behavior, and contract state to explain on-chain activity. Task-specific prediction systems assist investigators, while evidence collection and interpretation still require substantial expertise. We present Bgent, a multi-task blockchain investigation agent that combines tutorial-derived guidance with executable checks of factual claims. Offline distillation extracts tool operations and investigation procedures, producing a tool taxonomy and a reusable skill. At runtime, the investigator retrieves evidence and submits an answer with explicit factual claims. A planner selects checkable claims, and independent validators execute Python predicates over saved tool responses. Failed checks trigger revision within the same investigation session. Experiments on Ethereum cover account classification, attack-transaction detection, and smart-contract fault localization. Bgent achieves 96.45% mean F1 on valid attack-detection decisions and 56.86% Recall@1 in fault localization. Removing distilled guidance reduces account-classification F1 from 80.40% to 38.14%. Executable checking corrects specific factual errors in explanations while leaving the reported classification scores unchanged.