Jan 6th defendant wants video footage released

The Right to Discovery: Brady Material
Courts have held that the U.S. Constitution doesn’t impose a general duty on the prosecution to disclose “material” evidence to the defense. “Material” is generally shorthand for “relevant”; it’s often used to refer to evidence that, if disclosed, could affect the outcome of a case.
Exculpatory Evidence
The Constitution does, however, require that the prosecution disclose to the defense exculpatory evidence within its possession or control. “Exculpatory” generally means evidence that tends to contradict the defendant’s supposed guilt or that supports lesser punishment. The evidence doesn’t have to strongly indicate innocence in the way that an alibi, for example, would. It’s generally enough that the evidence provides significant aid to the defendant’s case. So, information that affects the credibility of a critical prosecution witness—like the fact that the prosecution offered its witness leniency in exchange for testimony—is among the kinds of evidence prosecutors have disclose. (Giglio v. United States, 405 U.S. 150 (1972).)
Defense attorneys routinely submit requests for discovery, and they make sure to ask for the above evidence, which often goes by “Brady material.” The government violates the law by not turning over this kind evidence, even if the failure to disclose wasn’t intentional or was beyond the prosecution’s control.

Brady v. Maryland

Brady v. Maryland was a 1963 U.S. Supreme Court case. In it the Court held that it’s a violation of due process for the prosecution to suppress evidence that the defense has requested and that is:

material either to guilt or punishment and
favorable to the accused.

In that case, Brady and Boblit had been convicted of first degree murder and sentenced to death. At his trial, Brady testified that he participated in the crime, but that Boblit actually killed the victim. Before trial his lawyer had requested that the prosecution give access to Boblit’s out-of-court statements. The defense saw several of those statements, but the prosecution withheld one, in which Boblit admitted carrying out the killing. The Court held that the prosecution’s action—even though it had to do with punishment rather than guilt—denied Brady the due process of law that’s guaranteed by the 14th Amendment. (Brady v. Maryland, 373 U.S. 83 (1963).)

Brady Violations
If the defense learns about a Brady violation after the defendant has been convicted, the defendant is typically owed a new trial if the nondisclosure was material. According to the U.S. Supreme Court, the missing evidence is to be considered as a whole rather than piece by piece, but it’s material only if there’s a “reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different.” (United States v. Bagley, 473 U.S. 667 (1985); Kyles v. Whitley, 514 U.S. 419 (1995).)
Courts have tended to be quicker to find Brady violations where the defense has specifically requested an item and the prosecution has misled the defense about its existence. Courts will find Brady violations in other circumstances too, as when the defense has made a very general request for exculpatory material or hasn’t made any request. But they might be slower to hold that the omission was material in these kinds of situations.

https://www.lawyers.com/legal-info/criminal/criminal-law-basics/criminal-law-right-to-evidence-disclosure.html