Cause-and-origin (C&O) reports are opinions, not facts. They can be challenged, and they often are. A modern defense to an arson C&O starts by testing the report against NFPA 921, the national standard for fire investigation. We look for outdated indicators ("alligatoring," "crazed glass," low burn patterns read as pour patterns, V-patterns read without ventilation analysis), gaps in ventilation analysis, failures to rule out electrical and smoking-materials causes, chain-of-custody issues on debris samples, and lab calibration problems. We then retain our own certified fire investigator - often a retired state fire marshal or a CFI - to reexamine the scene, the photographs, and the samples and write a rebuttal report. At trial, the jury hears both experts, and in a well-prepared defense, the state's expert often cannot survive cross-examination on the science. Bank & Munns has built arson defenses around C&O challenges many times.