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The crime of obstruction of justice, in United States jurisdictions, refers to the crime of interfering with the work of police, investigators, regulatory agencies, prosecutors, or other (usually government) officials. Common law jurisdictions other than the United States tend to use the wider offense of perverting the course of justice.
Generally, obstruction charges are laid when it is discovered that a person questioned in an investigation, other than a suspect, has lied to the investigating officers. However, in most common law jurisdictions, the right to remain silent allows any person questioned by police merely to refuse to answer questions posed by an investigator without giving any reason for doing so. (In such a case, the investigators may subpoena the witness to give testimony under oath in court, though the witness may then exercise their rights, for example in Fifth Amendment, if they believe their answer may serve to incriminate themselves). If the person lied to protect a suspect (such as by providing a false alibi, even if the suspect is in fact innocent) or to hide from investigation their own activities (such as to hide his involvement in another crime), this may leave them liable to prosecution. Obstruction charges can also be laid if a person alters or destroys physical evidence, even if he was under no compulsion at any time to produce such evidence. Often, no actual investigation or substantiated suspicion of a specific incident need exist to support a charge of obstruction of justice.
Obstruction can include crimes committed by judges, prosecutors, attorneys general, and elected officials in general. It is misfeasance, malfeasance or nonfeasance in the conduct of the office. Most commonly it is prosecuted as a crime for perjury by a non governmental official primarily because of prosecutorial discretion.
Modern obstruction of justice:
In United States v. Binion, malingering or feigning illness during a competency evaluation was held to be obstruction of justice and led to an enhanced sentence.

From Wiki.

Obstruction of justice is the crime of interfering with the work of law enforcers, such as police officers or investigators.