The procedure of the adversary system contemplates that the evidence in a case is to be marshalled competitively by the contending parties. Fair competition in the adversary system is secured by prohibitions against destruction or concealment of evidence, improperly influencing witnesses, obstructive tactics in discovery procedure, and the like.
 Documents and other items of evidence are often essential to establish a claim or defense. Subject to evidentiary privileges, the right of an opposing party, including the government, to obtain evidence through discovery or subpoena is an important procedural right. The exercise of that right can be frustrated if relevant material is altered, concealed or destroyed. Applicable law in many jurisdictions makes it an offense to destroy material for purpose of impairing its availability in a pending proceeding or one whose commencement can be foreseen. Falsifying evidence is also generally a criminal offense. Paragraph (a) applies to evidentiary material generally, including computerized information. Applicable law may permit a lawyer to take temporary possession of physical evidence of client crimes for the purpose of conducting a limited examination that will not alter or destroy material characteristics of the evidence. In such a case, applicable law may require the lawyer to turn the evidence over to the police or other prosecuting authority, depending on the circumstances.
 With regard to paragraph (b), it is not improper to pay a witness's expenses or to compensate an expert witness on terms permitted by law. The common law rule in most jurisdictions is that it is improper to pay an occurrence witness any fee for testifying and that it is improper to pay an expert witness a contingent fee.
 Paragraph (f) permits a lawyer to advise employees of a client to refrain from giving information to another party, for the employees may identify their interests with those of the client. See also Rule 4.2.