Yes, a co-defendant can be a witness against you, but only after their own Fifth Amendment protection against self-incrimination is out of the way. As long as they still face charges for the same conduct, they can refuse to answer questions on the stand. Prosecutors typically clear that barrier through a plea agreement, a court-ordered grant of immunity, or a severed trial that ends the co-defendant’s own jeopardy first.
Why the Fifth Amendment Usually Blocks Them First
The Fifth Amendment says no person can be forced to be a witness against themselves in a criminal case.1Justia. U.S. Constitution Annotated Fifth Amendment – Power to Compel Testimony and Disclosure For someone charged alongside you, that protection is broad. Almost any question about the events behind the charges could give the government ammunition against them, so they can refuse to answer prosecutors, defense lawyers, and the judge.
The privilege doesn’t end at the verdict. It stretches through sentencing, and as a practical matter it lasts until the co-defendant’s criminal exposure is genuinely finished, whether by acquittal, a completed sentence, or the running of the appeal period.2Justia. U.S. Constitution Annotated Fifth Amendment – Self-Incrimination Until then, no court can compel them to take the stand.
How Prosecutors Get a Co-Defendant to Testify Against You
Insider testimony is often the strongest evidence the government has, especially in conspiracy and organized crime cases. To use it, prosecutors have to neutralize the Fifth Amendment problem first. There are three main ways.
A Plea Deal
This is the most common path. The co-defendant pleads guilty, often to reduced charges, and the prosecution recommends a lighter sentence in return. Once the court accepts the plea, their liability for the charged conduct is settled, and the Fifth Amendment no longer stops them from talking. The government may then also move for a further sentencing reduction based on the value of their cooperation, which gives them a strong reason to give useful testimony.
A Grant of Immunity
When a plea deal isn’t the right fit, prosecutors can ask a judge to order the witness to testify under immunity. Once that order issues, the witness can no longer refuse to answer on Fifth Amendment grounds. In exchange, nothing they say, and no evidence derived from what they say, can be used against them in a later criminal case.3Office of the Law Revision Counsel. 18 USC 6002 – Immunity of Witnesses The one exception is a prosecution for perjury or false statements during that immunized testimony.
This is called use and derivative use immunity, and it is the federal standard. The Supreme Court held in Kastigar v. United States that it satisfies the Fifth Amendment because it leaves the witness in essentially the same position as if they had stayed silent; if the government later prosecutes them for the same crime, it must prove every piece of its evidence came from a source independent of the compelled testimony.4Justia. Kastigar v United States 406 US 441 (1972) A broader form, transactional immunity, blocks any prosecution for the events testified about; the Court in Kastigar made clear this goes further than the Constitution requires. Some states still use it, but the federal system does not.
Separate Trials
A judge can sever co-defendants’ trials when a joint proceeding would unfairly prejudice one of them.5Legal Information Institute. Federal Rules of Criminal Procedure Rule 14 – Relief from Prejudicial Joinder If the co-defendant’s trial finishes first and ends in either a conviction or acquittal, their jeopardy on those charges is over. From that point, they can be called as a witness in the remaining trial, because the Fifth Amendment no longer applies to the resolved charges.
Proffer Sessions Come Before the Deal
Before a formal cooperation agreement exists, prosecutors and a would-be cooperator often meet in what’s called a proffer session, sometimes “queen for a day.” The co-defendant, usually with their lawyer present, previews what they know. A written proffer agreement controls the session, and the protection is narrower than most people assume.
The agreement typically bars prosecutors from using the actual words from the session as direct evidence at trial. It does not stop them from following leads and using whatever independent evidence those leads turn up. It also lets prosecutors use the proffer statements to impeach the witness if they later say something different, and some modern versions allow use against the co-defendant whenever their trial defense contradicts what they said in the session. Nothing in a standard proffer agreement guarantees immunity or a plea. If the information pans out, a cooperation deal usually follows. If it doesn’t, the co-defendant has handed the government a roadmap.
Can a Co-Defendant Testify for the Defense Instead
You have the right to call witnesses in your favor, but that right doesn’t override someone else’s Fifth Amendment protection. If your co-defendant’s testimony could incriminate them, they can refuse, and the court will honor that refusal. No judge will force another person to waive a constitutional right to help your case. That is why defense calls of a co-defendant are rare unless their case is already resolved or the specific testimony carries no self-incrimination risk. In most situations, the co-defendant’s lawyer will advise taking the Fifth, and that is the end of it.
When the Co-Defendant Doesn’t Testify but Their Confession Names You
The flip side can be just as damaging. If your co-defendant confessed to police and doesn’t take the stand at a joint trial, the prosecution may want to introduce that confession. The Sixth Amendment gives you the right to confront and cross-examine the witnesses against you, and a non-testifying co-defendant can’t be cross-examined.
In Bruton v. United States, the Supreme Court held that admitting a non-testifying co-defendant’s confession that implicates you violates the Confrontation Clause, even if the judge tells the jury to consider it only against the person who made it.6Justia. Bruton v United States 391 US 123 (1968) The Court recognized that some instructions ask too much of jurors. When the confession is detailed and points straight at the other defendant, telling the jury to ignore it is not a realistic safeguard.
Prosecutors have three usual responses: try the defendants separately, leave the confession out, or redact it. In Samia v. United States (2023), the Court held that a redacted confession replacing the defendant’s name with a neutral term like “another person” does not violate the Confrontation Clause, provided the jury is instructed to use the statement only against the confessing co-defendant. The line is between a confession that names you and one genuinely scrubbed of identifying details.
How the Defense Attacks Cooperating Testimony
Cooperating co-defendants are powerful witnesses and also easy targets. They have firsthand knowledge, which makes their testimony compelling. They also have an obvious motive to say whatever keeps their deal alive, which makes it suspect.
Courts recognize the tension. Judges routinely instruct juries to weigh accomplice testimony with special caution, and some states require independent corroborating evidence connecting the defendant to the crime before a conviction can rest on accomplice testimony alone.
Cross-examination is where these cases turn. A defense lawyer will lay out every benefit the witness received: reduced charges, sentencing recommendations, counts dropped. If there was a proffer, any inconsistency between what was said then and what is being said now becomes fair game. Jurors understand self-interest, and a skilled cross can reframe a cooperation deal as a transaction rather than a search for the truth.
What Keeps the Witness Honest
A co-defendant who testifies under oath, whether under a plea deal or an immunity order, faces real consequences for lying. Federal perjury carries a maximum of five years in prison.7Office of the Law Revision Counsel. 18 USC 1621 – Perjury Generally State penalties vary, typically five to ten years. An immunity grant explicitly does not cover perjury, so a witness who lies under immunity loses nothing on the front end and picks up a new felony.3Office of the Law Revision Counsel. 18 USC 6002 – Immunity of Witnesses
For a witness with a plea agreement, lying is also a breach. The government can void the deal, reinstate dismissed charges, withdraw its recommendation for a reduced sentence, and use the co-defendant’s own cooperation statements against them. Courts hold evidentiary hearings to decide whether a breach occurred. That threat cuts both ways at trial: it gives the jury a reason to trust the testimony, and it gives the defense a reason to argue the witness is locked into telling the version the government wants.