Obstruction of justice is an attempt to interfere with the administration of the courts, the judicial system or law enforcement officers. It may include tampering with or intimidating, hiding evidence or interfering with an arrest. It is something a person does to impede the administration of a court process or proper discharge of a legal duty. Interference may be with the work of police, investigators, regulatory agencies, prosecutors, or other (usually government) officials. Often, no actual investigation or substantiated suspicion of a specific incident need exist to support a charge of obstruction of justice. Such activity is a crime.
The crime of threatening a witness in federal cases is defined by statute at 18 U.S.C. § 1512, "Tampering with a witness, victim, or an informant". The punishment for such an offense is up to 20 years if physical force was used or attempted, and up to 10 years if physical force was only threatened.