Suppression of witnesses or evidence occurs when a prosecutor deliberately withholds, conceals, or obstructs access to testimony, documents, physical items, or other material information that is favorable to the defense, relevant to guilt or punishment, or necessary for a fair adjudication. Such conduct directly violates due process and undermines the integrity of judicial proceedings.

**Scope:**

- **Witness Suppression**: Preventing defense access to witnesses, discouraging witnesses from testifying, or failing to disclose witness identities.
- **Evidence Withholding**: Concealing exculpatory or mitigating material, even if not requested by the defense.
- **Access Obstruction**: Imposing improper restrictions on discovery, delaying disclosure to limit effective use at trial, or providing evidence in unusable formats.
- **Non-Disclosure of Impeachment Evidence**: Withholding information that would undermine the credibility of a government witness, law enforcement officer, or expert.

**Examples:**

- Failing to disclose that a key eyewitness recanted testimony.
- Concealing a forensic lab report that excludes the defendant as a DNA match.
- Instructing police to withhold notes or recordings that contradict trial testimony.

**Related Standards:**

- **Brady v. Maryland, 373 U.S. 83 (1963)**: Requires disclosure of exculpatory evidence.
- **Giglio v. United States, 405 U.S. 150 (1972)**: Extends disclosure to impeachment material.
- **Kyles v. Whitley, 514 U.S. 419 (1995)**: Prosecutors are responsible for evidence in possession of the government, even if not personally aware.
- **ABA Model Rule 3.8(d)**: Prosecutors must timely disclose evidence that negates guilt or mitigates offense.

**Consequences:**  
Suppression of witnesses or evidence can result in reversal of convictions, dismissal of charges, professional sanctions, contempt findings, and erosion of prosecutorial credibility.