Legal Issues, Liability, and Expert Testimony
Legal framework
Expert testimony must be reliable and relevant. Daubert (federal) requires the court to assess methodology - testability, error rate, peer review, and general acceptance - while Frye (some states) requires general acceptance. An expert must be qualified by knowledge, skill, experience, training, or education and must disclose the basis for opinions. Government investigators are subject to the Fourth Amendment; Michigan v. Tyler held that a warrant is generally required for re-entry once the initial exigency ends, though consent, plain view, and exigent circumstances can still apply.
Liability and evidence
Spoliation is destruction or alteration of evidence that prejudices another party; preserve everything relevant. Chain of custody affects admissibility. Arson is a specific-intent crime requiring proof of malice; an investigator's finding of "incendiary" is not a finding of arson. Be aware of product liability, insurance fraud, and subrogation contexts that shape the investigation.
TRAP: Assuming an investigator may re-enter without consent or a warrant, or conflating "incendiary" with "arson."
RULE OF THUMB: Write every opinion the way you would say it on the witness stand, and assume opposing counsel will read every note you take.