Wiktionary
n. Talking to a witness, hoping for them to lie, or change their opinion, about what really happened.
Wikipedia
Witness tampering is the act of attempting to alter or prevent the testimony of witnesses within criminal or civil proceedings. Laws regarding witness tampering also apply to proceedings before Congress, executive departments, and administrative agencies. To be charged with witness tampering in the United States, the attempt to alter or prevent testimony is sufficient. There is no requirement that the intended obstruction of justice be completed.
In situations where intimidation or retaliation against witnesses is likely (such as cases involving organized crime), witnesses may be placed in witness protection to prevent suspects or their colleagues intimidating them.
In the United Kingdom, witness intimidation is covered by Criminal Justice and Public Order Act 1994, section 51. Under this act it is an offence to perform an act which is intended to and does intimidate a person who the offender knows or believes to be involved with a criminal case with the intention of disturbing the proceedings.
Usage examples of "witness tampering".
Criminal methods - perjury, obstruction of justice, witness tampering, using the instruments of federal government to intimidate witnesses - all these have been shown to work.
Nobody from the Amazing Kingdom bothered to check with previous employers, such as the New York City Police Department, to inquire about allegations of bribery, moral turpitude, substance abuse, witness tampering and the unnecessary use of deadly force, to wit, the pistol-whipping of a young man suspected of shoplifting a bag of cheese-flavored Doritos.