Yes. In federal criminal cases, the defense does have to disclose evidence to the prosecution, but only in narrow, defined categories and only after the defense first asks the prosecution for discovery. The obligation is reciprocal, meaning it turns on what the defense has requested and what it plans to put on at trial. It is not a general duty to open the file.
When the Duty Kicks In
The defense’s obligation to share evidence is not automatic. It begins only after the defense formally requests discovery from the prosecution and the prosecution complies. At that point, the prosecution can request comparable information in return.
The constitutional foundation comes from Wardius v. Oregon, where the Supreme Court held that “discovery must be a two-way street” and that the government cannot demand the defense reveal its case while keeping its own witnesses secret.1LII / Legal Information Institute. Wardius v. Oregon The defense can be required to disclose, but only because the prosecution has already offered reciprocal access to its own evidence.
What the Defense Must Turn Over
Federal Rule of Criminal Procedure 16 sets out three categories. Each is limited to evidence the defense actually plans to present during its case-in-chief.
Documents and Physical Evidence
Any documents, photographs, or other tangible items the defense plans to introduce at trial must be made available to the prosecution for inspection and copying. That covers things like receipts, contracts, emails, or surveillance footage. The item has to be within the defendant’s possession or control, and the defense must intend to use it in its case-in-chief.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection
Scientific Tests and Examination Reports
Results from any physical or mental examination or scientific test the defense plans to use at trial must be shared with the prosecution. That includes independent forensic analysis, defense-conducted DNA testing, or a psychological evaluation of the defendant. Disclosure is also required when the defense intends to call the person who prepared the report and the report relates to that testimony.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection
Expert Witness Summaries
The defense must provide a written summary of any expert testimony it plans to present during its case-in-chief. The summary has to describe the expert’s opinions, the bases and reasons for those opinions, and the expert’s qualifications.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection This gives the prosecution time to line up its own expert or prepare cross-examination.
Special Notices for Certain Defenses
Separate rules require advance written notice when the defense plans to rely on certain defenses. These exist because the prosecution needs time to investigate or bring in its own experts.
Alibi
If the defendant plans to argue they were somewhere else when the crime occurred, the defense must file a written notice stating the specific location and the name, address, and telephone number of each alibi witness. The notice must be served within 14 days of the prosecution’s request, unless the court sets a different deadline. Once the defense provides the notice, the prosecution must disclose the names of its own witnesses who will place the defendant at the scene and any rebuttal witnesses it plans to call against the alibi.3LII / Legal Information Institute. Federal Rules of Criminal Procedure Rule 12.1 – Notice of an Alibi Defense
Insanity and Mental Condition
A defendant who intends to assert an insanity defense must notify the prosecution in writing and file a copy with the court clerk. Skipping this notice bars the defense at trial, though a court can grant a late filing for good cause.4LII / Legal Information Institute. Federal Rules of Criminal Procedure Rule 12.2 – Notice of an Insanity Defense and Mental Examination
A related requirement applies when the defense plans to introduce expert testimony about the defendant’s mental condition bearing on guilt or punishment. The defense must notify the prosecution in writing, and after the government conducts its own examination, the defense must disclose the results of any examination by its own expert that it intends to present at trial. Non-compliance can result in the expert testimony being excluded.4LII / Legal Information Institute. Federal Rules of Criminal Procedure Rule 12.2 – Notice of an Insanity Defense and Mental Examination
What the Defense Does Not Have to Share
This is where the defense’s obligation is much narrower than people often assume.
Anything Outside the Case-in-Chief
Rule 16 applies only to evidence the defense intends to use in its case-in-chief, the portion of trial where the defense presents its own evidence after the prosecution rests.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection Evidence the defense plans to use only to cross-examine or impeach prosecution witnesses generally falls outside this obligation. If the defense holds a document that would undermine a prosecution witness’s credibility but does not plan to introduce it during its own case, it typically does not have to disclose it under Rule 16.
Attorney-Client Communications
Confidential communications between a defendant and their lawyer are off-limits. If a defendant tells their lawyer where they were on the night in question, that conversation is privileged even if the defense later decides not to present an alibi.
Attorney Work Product
Materials the defense attorney prepares while working on the case, including legal research, strategic memos, and internal notes about the strengths and weaknesses of the prosecution’s evidence, are protected as work product. The protection extends to materials prepared by investigators or consultants working for the defense team.
Defense-Generated Statements and Reports
Rule 16 specifically excludes reports, memos, and other documents created by the defendant or their attorney during the investigation. The same goes for statements made to the defense team by the defendant, witnesses, or prospective witnesses. The one exception is scientific or medical reports, which must be disclosed if the defense plans to use them at trial.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection
Anything Covered by the Fifth Amendment
A defendant cannot be compelled to testify, provide a written statement, or generate evidence against themselves.5LII / Legal Information Institute. Fifth Amendment Reciprocal discovery is constitutional precisely because it reaches only evidence the defense has chosen to put on at trial.
Witness Statements Produced During Trial
One disclosure duty arises during trial rather than before it. Under Federal Rule of Criminal Procedure 26.2, after a defense witness finishes testifying on direct examination, the prosecution can ask the court to order the defense to produce any prior written or recorded statements that witness made, as long as they relate to the subject of the testimony.6Cornell Law School. Federal Rules of Criminal Procedure Rule 26.2 – Producing a Witness’s Statement Refusal carries a heavy penalty: the court must strike the witness’s entire testimony. The rule cuts both ways, so the defense can demand the same for prosecution witnesses.
The Duty Continues Through Trial
Under Rule 16(c), if either side discovers additional evidence before or during trial that falls within a prior discovery request, it must promptly disclose that evidence.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection A defense team that uncovers a new expert report or locates an additional document two weeks before trial cannot sit on it.
Protective Orders for Sensitive Material
Sometimes evidence subject to discovery involves the identity of a confidential witness, matters touching on national security, or material that could put someone in danger. Either side can ask for a protective order. Under Rule 16(d)(1), a judge can deny, restrict, or delay discovery for good cause. The party seeking protection can make its case through a written statement the judge reviews privately, and if the court grants relief on that showing, it must seal the statement so an appellate court can review it later.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection
Penalties for Not Disclosing
When the defense violates a discovery obligation, Rule 16(d)(2) gives the court several options:
- Order the defense to produce the evidence and set a deadline for doing so.
- Grant the prosecution a continuance to prepare for the newly revealed evidence.
- Exclude the undisclosed evidence at trial, which can gut a defense theory.
- Enter any other just order, a catch-all that gives judges broad discretion.
The rule does not specifically list mistrial or contempt, but the catch-all provision leaves room for those remedies in extreme cases.2Cornell Law Institute. Federal Rules of Criminal Procedure Rule 16 – Discovery and Inspection Exclusion of defense evidence sits in tension with the Sixth Amendment’s Compulsory Process Clause, and in Taylor v. Illinois the Supreme Court held that excluding defense witnesses as a discovery sanction is not absolutely prohibited, but courts typically reserve it for willful violations or situations where the prosecution would suffer genuine prejudice.
A Note on State Court
Everything above applies to federal criminal cases. State rules follow the same reciprocal principle but vary considerably in how much the defense must share. Some states track the narrower federal model; others require both sides to share significantly more, including witness lists and summaries of expected testimony well before trial. If you are facing charges in state court, the specific deadlines and categories will depend on that state’s procedural rules.