A motion for discovery in a criminal case is a formal written request asking the judge to order the prosecution to turn over specific evidence before trial. The defense almost always files it. The purpose is simple: a defendant should not meet the government’s evidence for the first time in front of a jury. What the motion actually produces, though, is narrower than most people expect, and knowing those limits matters as much as knowing the rules.
What the Defense Can Ask For
In federal court, Rule 16 of the Federal Rules of Criminal Procedure sets the categories. Once the defense requests them, the government must produce:
- Any written or recorded statement the defendant made that is in the government’s possession, if the prosecution knows or reasonably should know it exists.
- A copy of the defendant’s prior criminal record.
- Documents, photographs, data, and tangible objects the government plans to use at trial, that are material to the defense, or that were obtained from the defendant.
- Results of any physical or mental examination, DNA analysis, fingerprint comparison, toxicology screening, or other scientific test, if the material is relevant to the defense or will be used at trial.
- A written summary of any expert testimony the prosecution plans to present, including the expert’s opinions, the reasoning behind those opinions, and the expert’s qualifications.
None of this moves automatically. Each category requires a request from the defense to trigger the government’s duty to disclose.1Legal Information Institute. Federal Rules of Criminal Procedure – Rule 16 Discovery and Inspection
What a Discovery Motion Cannot Reach
Two large categories of evidence sit outside standard pretrial discovery, and this is where expectations most often collide with reality.
Internal Government Work Product
Rule 16 specifically excludes “reports, memoranda, or other internal government documents made by an attorney for the government or other government agent in connection with investigating or prosecuting the case.”1Legal Information Institute. Federal Rules of Criminal Procedure – Rule 16 Discovery and Inspection Prosecution strategy notes, internal legal memos, and investigative assessments stay with the government.
Statements of Government Witnesses
Under the Jencks Act, the prior statements of a government witness cannot be obtained through discovery or subpoena “until said witness has testified on direct examination in the trial of the case.” Only after the witness steps down from direct can the defense ask for that witness’s recorded statements. The judge then gives the defense time to review the material for cross-examination. If the government refuses to produce a statement after being ordered to, the court must strike the witness’s testimony and can declare a mistrial if justice requires it.2Office of the Law Revision Counsel. 18 USC 3500 – Demands for Production of Statements and Reports of Witnesses
The practical consequence is sharp. In federal court, the defense often does not know what a key witness will actually say until that witness is on the stand.
What the Prosecution Must Hand Over Even Without a Motion
Separate from Rule 16, the prosecution carries a constitutional duty to disclose certain evidence on its own, motion or no motion. This duty sometimes gets lumped in with discovery, but it operates differently and reaches further.
In Brady v. Maryland, the Supreme Court held that “the suppression by the prosecution of evidence favorable to an accused upon request violates due process where the evidence is material either to guilt or to punishment, irrespective of the good faith or bad faith of the prosecution.”3Justia. Brady v. Maryland, 373 US 83 (1963) Favorable evidence means anything that points toward innocence or could reduce the sentence. The prosecutor’s intent is irrelevant; an honest oversight still counts.
In United States v. Bagley, the Court defined “material” evidence as evidence creating “a reasonable probability that, had the evidence been disclosed to the defense, the result of the proceeding would have been different.”4Justia. United States v. Bagley, 473 US 667 (1985)
Giglio v. United States extended the duty to impeachment evidence: deals made with witnesses, prior convictions, bias, or anything else that would give a jury reason to doubt a witness’s credibility.5Justia. Giglio v. United States, 405 US 150 (1972) And in Kyles v. Whitley, the Court held that “the individual prosecutor has a duty to learn of any favorable evidence known to the others acting on the government’s behalf in the case, including the police.”6Legal Information Institute. Kyles v. Whitley, 514 US 419 (1995) A detective who sits on exculpatory evidence is a problem the prosecutor owns.
What the Defense Has To Share Back
Discovery runs both ways. Once the defense requests and receives documents, physical evidence, or scientific reports from the government, the prosecution can request the same categories in return.1Legal Information Institute. Federal Rules of Criminal Procedure – Rule 16 Discovery and Inspection The defense must also produce a written summary of any expert testimony it plans to introduce.
This reciprocal duty is narrow. The Fifth Amendment keeps the prosecution from using discovery to pry incriminating information out of the defendant. What the defense must share is limited to items it intends to use at trial.
Filing the Motion and the Timing That Matters
After arraignment, attorneys on both sides often start exchanging basic evidence informally. The prosecution has an ongoing duty to provide the defense with evidence it plans to use at trial, and a lot of material changes hands without any motion being filed.7United States Department of Justice. Discovery
When informal exchange stalls, the defense files a formal motion identifying the specific categories of evidence requested and explaining why the material is relevant. Discovery motions must generally be raised before trial if the basis for the motion is reasonably available at that time. The court typically sets a pretrial motion deadline at or shortly after arraignment; if it doesn’t, the default is the start of trial.8Legal Information Institute. Federal Rules of Criminal Procedure – Rule 12 Pleadings and Pretrial Motions
Missing the deadline is not automatically fatal. A court can still consider a late motion if the defense shows good cause, such as learning of grounds that weren’t previously available.8Legal Information Institute. Federal Rules of Criminal Procedure – Rule 12 Pleadings and Pretrial Motions If the court grants the motion, it issues an order specifying the time, place, and manner of the exchange.
When the Other Side Doesn’t Comply
If the prosecution ignores a discovery request or withholds material it was ordered to produce, the defense’s next step is a motion to compel. Rule 16(d)(2) gives the judge several options:
- Order the noncompliant party to produce the evidence on specific terms.
- Grant a continuance so the other side can review late-disclosed material.
- Bar the noncompliant party from using the withheld evidence at trial.
- Enter any other order the court finds just, which in serious cases can include a mistrial or dismissal of charges.
These sanctions apply to both sides. A defense team that ignores its reciprocal obligations faces the same consequences.1Legal Information Institute. Federal Rules of Criminal Procedure – Rule 16 Discovery and Inspection
Brady violations run on a separate track. Because the duty to disclose favorable evidence is constitutional, the remedy can reach far past trial. A defendant who later shows that the prosecution suppressed material favorable evidence may be entitled to a new trial, sometimes years after conviction, if the undisclosed evidence would have created a reasonable probability of a different outcome.4Justia. United States v. Bagley, 473 US 667 (1985)
State Court Can Look Very Different
Everything above describes federal practice. State discovery rules vary widely, and in many states the defense receives significantly more than Rule 16 provides.
Roughly a third of states have adopted broader discovery modeled on American Bar Association standards, requiring prosecutors to disclose witness lists, witness statements, and favorable evidence before trial. A smaller but growing group of states uses “open file” discovery, where the defense gets access to essentially everything in the prosecution’s file except privileged work product. Other states historically kept pretrial discovery narrow, closer to the federal model.
The difference is practical, not academic. In a federal case, a defense attorney may not see a witness’s prior statement until that witness is already testifying. In an open-file state, that same statement may arrive weeks before trial. If you’re facing criminal charges, one of the first things to ask a defense lawyer is what the discovery rules in your jurisdiction actually allow you to see, and when.