DR 7-109 Contact with Witnesses.

1. A lawyer shall not suppress any evidence that he or his client has legal obligation to reveal or produce.
2. A lawyer shall not advise or cause a person to secrete himself or to leave the jurisdiction of a tribunal for the purpose of making him unavailable a witness therein.
3. A lawyer shall not pay, offer to pay, or acquiesce in the payment of compensation to a witness contingent upon the content of his testimony or the outcome of the case. But a lawyer may advance, guarantee, or acquiesce in the payment of:

1. Expenses reasonably incurred by a witness in attending or testifying.
2. Reasonable compensation to a witness for his loss of time in attending or testifying.
3. A reasonable fee for the professional services of an expert witness.