Obstruction of justice covers a range of acts that impede law enforcement or agency investigations. Under 18 U.S.C. § 1505, it is a federal crime to obstruct proceedings before federal agencies such as the NTSB. Related charges include making false statements to federal investigators (18 U.S.C. § 1001) and tampering with evidence. Obstruction charges are often added when prosecutors believe the original crime was compounded by a cover-up — the obstruction itself becomes a separate criminal act regardless of whether the underlying conduct is proven.