How to Prepare for Testifying Against Co-Defendants.

Last Updated on: 4th August 2026, 01:33 am

Here are some tips for preparing to testify against co-defendants:

1. Never Lie and Do Not Guess

Witnesses who testify in federal criminal trials in the United States ordinarily swear or affirm that their testimony will be “truthful and the truth, the whole truth, and nothing but the truth.” If you do not have personal knowledge of a fact or do not know the answer to a question, do not guess. Instead, say, “I don’t know,” or a similar appropriate statement.

2. Be Thorough About Familiarizing Yourself With the Case

Before trial, familiarize yourself thoroughly with the case and review all relevant prior interview transcripts, testimony, reports, exhibits, and any other pertinent materials.

3. Do Not Meet With the Government’s Attorneys Without Your Independent Counsel Present

If you have signed a cooperation agreement with the government as a cooperating witness, do not attend any meetings with the government’s attorneys without independent counsel.

4. Be Prepared for the Process of Testifying and Questioning at Trial

Direct examination is the examination of a witness by the attorney who called the witness to testify. Direct examination is usually followed by cross-examination and, in some cases, a redirect examination. After this process, you may be recalled for further questioning, or the government may call upon a witness to testify before it rests its case. Objections and questions from other attorneys will interrupt your testimony while the judge makes a decision on whether you should be permitted to answer.

You will also need to know when to stop talking. You will also need to know what to do when a witness has already answered the question, and when to say, “I already answered that question.”

Note: Federal Rules of Evidence do not govern testimony in state court cases, and similar rules may (or may not) exist in state courts.

Can Lawyers Prepare Me Without Telling Me What to Say?

Yes, lawyers can prepare witnesses to testify in federal cases without violating any ethical rules. In fact, witness preparation is an essential part of a criminal defense attorney’s job. Witnesses who have properly prepared can deliver a truthful and coherent narrative that can assist a judge or jury in seeing the truth in any criminal case.

Witnesses who are prepared to testify against co-defendants should never feel like they have to concoct a false account of events. Similarly, witnesses should not feel any pressure to coordinate false accounts with other witnesses. There should be no attempt to lie, fabricate evidence, or misrepresent material. Even if a witness is facing serious legal consequences that could lead him or her to do so, preparing to testify against a co-defendant should never involve concocting or coordinating any form of false information.

Instead, witness preparation should center on strengthening their testimony so it is as convincing and straightforward as possible. This starts by establishing a witness’s understanding of the issues that will be at play at trial. With that in place, the lawyer will be able to identify the topics on which the witness will need to provide information and, therefore, identify which questions may be asked during a direct examination.

At the same time, witnesses need to be prepared for the possibility of cross-examination from opposing counsel. This will be an adversarial process. It is imperative that a witness be as prepared as possible to deliver consistent, and believable testimony when asked to do so under pressure. At the same time, witnesses will also need to know when to object, when to stop talking, and when they have already answered a question so they may not have to provide the answer twice.

Memorizing an answer can be harmful because it often makes a witness look rehearsed, which can undermine the believability of the testimony. The witness should understand the facts and what they will say to help deliver the answer to a question. If the answer is provided exactly as rehearsed, and the question does not match the rehearsed question, it can lead to a confusing answer that may be used to cast doubt upon the witness’s testimony.

Inconsistency is a major vulnerability during cross-examination. If a witness made a statement in the past that is not consistent with their testimony at trial, opposing lawyers will use this to cast doubt. However, inconsistency on its own does not equal dishonesty. Mistakes or errors can be made for many reasons, such as not fully understanding the questions asked, not knowing all relevant facts, or getting confused during questioning. Therefore, witnesses should review their prior statements and discussing any potential errors with their lawyer before trial.

Federal Rule of Evidence 613 (prior inconsistent statements) gives witnesses who have prior inconsistencies the chance to explain and/or deny their statements when required. This means witnesses can

What Should I Say and Avoid While Testifying Against a Co-Defendant?

There is no cited evidence that suggests that in fact 80% of the words spoken in a trial come from the lawyers, and 20% of the words come from the witness, meaning that, unless proven otherwise, this is simply false. Even so, there should never be any hesitation for a witness to clarify their answers if they feel that it will not harm their testimony.

Witnesses who testify against co-defendants should give direct answers, and that does not mean an evasive or incomplete answer. Rather, witnesses should deliver complete answers, and this means not only for the direct examination but for cross-examination as well. Even if the answer to the question is not permitted, the witness must always maintain a certain level of attentiveness to the trial proceedings.

If you do not understand a question that has been asked, you may request a clarification, which is a matter of understanding and not a matter of answering. If you do not remember a specific piece of information, you will also need to convey this in your response, as this is how witnesses will avoid any form of a perjury charge.

If you do not remember any specific part of your prior statements, or if you are not familiar with a question, you may politely ask for a clarification or the repetition of a question. Similarly, if you have mistakenly given an answer to a question, then you should politely state a correction. This not only will correct the error, but it will also help avoid any potential perjury accusations.

If a lawyer or other person provides an incorrect summary of your prior statements during your witness examination or if there are other inconsistencies in your answers, this needs to be addressed immediately. If errors are not addressed right away, they will reflect as inconsistent testimony, which opposing lawyers will then use during cross-examination to make you appear untrustworthy.

Rule 603 of the Federal Rules of Evidence requires a witness to give an oath or affirmation to testify truthfully. It is imperative that you not commit perjury while you are testifying, and if you swear or affirm that you will tell the truth, then you should prepare and deliver truthful testimony during the witness examination process.

Once a lawyer objects to a particular question, you must wait for the judge to make a decision and tell you whether answering is permitted. If the judge states, “Objection sustained,” then answering to the question will not be permitted. If the judge states, “Overruled,” you will be able to answer the question as asked.

18 U.S.C. §1827 states: “An interpreter shall be furnished to any person who: (A) does not speak or understand the English language, or (B) otherwise is not able to communicate with courts, judges, or other federal officers, or with the public, of the United States... due to a language barrier, or because of a lack of educational or academic training.”

“Witnesses should not quarrel with the questioning attorney.” While it is important that witnesses provide consistent and truthful testimony, they should not enter into an argument with opposing lawyers. As witnesses, if you believe that the lawyer is asking an improper question, you may raise this with your own lawyer.

How Will Defense Lawyers Attack My Credibility?

In most cases involving the use of prior statements of government witnesses, a proffer letter determines the permissible use of a witness’s prior statements. Usually, a proffer agreement generally prohibits using the proffer statement as substantive evidence in the government’s case against a defendant. However, the proffer statement may be used in the government’s case in certain circumstances, and, in some cases, it may be used to impeach the credibility of the witness.

The purpose of a proffer statement is to make the witness fully comfortable sharing relevant information with the government, and the witness’s proffer agreement will also state what the government can and cannot do with the witness’s statement. If the government intends to rely on the proffer statement, the witness’s proffer agreement will need to provide for the government’s use of the proffer statement as a direct, indirect, or implied admission.

The most common uses of a witness’s statement in a proffer are in cases where the witness testifies at the witness examination and makes a statement that is materially inconsistent with what was said in the proffer statement. Even though the proffer agreement may generally prohibit using the statement as a substantive piece of evidence, the material inconsistency allows for the possibility that the witness’s credibility should be questioned, and the proffer statement may be used for the purposes of impeachment during the witness’s cross-examination.

Common areas where a witness’s credibility will be attacked include the benefits the witness may have received or sought, any crimes committed, any prior lies, lies during the trial, motives for testifying, bias against the defendant, and inconsistencies between prior statements.

If the government entered into a cooperation agreement with a witness, this is evidence of a potential for bias. Even if the cooperation agreement did not award the witness any benefits, this fact can still be used to impeach a witness’s credibility.

If a witness testifies in support of the government’s case as a government witness, the defense will ask what he or she believes he or she is entitled to in terms of leniency and if this will come from a cooperation agreement. The witness will need to address whether the witness made a promise to give a false account and what he or she hopes to receive. This is part of a general strategy to cast doubt on a witness’s credibility.

In Giglio, the U.S. Supreme Court found that “promises made to a government witness in exchange for testifying can be material to a defendant’s case in determining the witness’s credibility, which could be relevant information for the witness’s reliability.” If the information is material, the government should disclose the information to the defense counsel.

18 U.S.C. §3500 mandates that, in most cases, covered witness statements will be supplied to a defendant’s counsel upon their request. Under the Federal Rules of Criminal Procedure, a party that did not call a witness may, after the witness testifies on direct examination, move to obtain the witness’s qualifying statement. The rules specify the types of proceedings they cover and the types of statements that need to be disclosed. Usually, a witness statement is any written statement given to the federal government, and the statement should not contradict the federal government’s presentation of a witness statement.

Spodek Law Group, led by managing partner Todd Spodek, defends clients in federal criminal and white collar matters.

What Can My Cooperation Agreement Actually Do for Sentencing?

Cooperation agreements typically include a provision where the prosecutors in the case make a nonbinding recommendation for a shorter sentencing term to the sentencing judge, even if the agreement includes a binding obligation of the government’s prosecutor to file a motion for sentencing reduction based on substantial assistance. Even with a binding obligation to file such a motion, the government’s prosecutor’s recommendation only applies to the sentencing judge’s sentencing opinion and not the actual sentence.

U.S.S.G. §5K1.1 provides that, upon a government motion stating that the defendant provided substantial assistance, a sentence below the otherwise applicable guideline range may be appropriate. The government prosecutor, when filing a motion pursuant to U.S.S.G. §5K1.1, will usually include a nonbinding recommendation for a shorter sentencing term. For the sentencing judge to grant this downward departure, he or she must agree that a substantial assistance departure is warranted under the Federal Sentencing Guidelines.

The U.S. Sentencing Guidelines are the sentencing rules that a judge may apply when sentencing a defendant. U.S.S.G. §5K1.1, is different from 18 U.S.C. §3553(e), which is a separate statutory provision allowing for sentencing below a statutory minimum. If the prosecuting federal attorney files a motion under 18 U.S.C. § 3553(e), the court may impose a sentence below a statutory minimum to reflect the defendant’s substantial assistance.

Again, while the prosecution attorney’s motion is required for a substantial assistance sentence, the motion itself is not binding for the sentencing judge. The sentencing judge determines the extent of the sentencing reduction.

While cooperation is essential to filing a motion under U.S.S.G. §5K1.1, it is not sufficient on its own. While the witness’s knowledge or testimony may be relevant to the prosecution’s case, prosecutors will only file a motion for a downward departure for substantial assistance when the information helps to get a conviction or secures a guilty plea.

While witnesses provide a key for a prosecutor to seek a §5K1.1, there may be numerous factors that could prevent a witness’s information from being used in court. The truthfulness of the witness’s information or the credibility of the witness’s information are important factors as well.

Witnesses who work with the government often have to work under a cooperation agreement which will also include benefits for the cooperating witness. Usually, cooperation agreements will include stipulations that require witnesses to be truthful and provide complete information to the government. If a witness fails to provide this information or if he or she is found to lie, it can result in a breach of the cooperation agreement. The breach of the agreement does not necessarily mean a witness will have to withdraw his or her plea; however, the government may lose the ability to argue for a reduced sentencing term in court.

If a witness is testifying under a cooperation agreement, a failure to provide truthful or complete information will only harm the witness and not the potential target of the prosecution.

Wait until after sentencing to seek reduced sentence after witnessing in criminal proceedings and for those sentenced under the government’s sentencing recommendation for a reduction in sentencing based on substantial assistance rendered to the government. This is provided for in Rule 35(b) of the Federal Rules of Criminal Procedure, which states that “[u]pon the government’s motion made within one year of sentencing, the court may reduce a sentence if the defendant, after sentencing, provided substantial assistance in investigating or prosecuting another person.” The prosecutors must file a motion under Rule 35(b) as well.

Can My Testimony Expose Me to New Criminal Charges?

Witnesses are protected from being forced to answer questions that present a “genuine risk of self-incrimination” under the Fifth Amendment. However, there are two major exceptions to the Fifth Amendment right to refuse to answer questions:

1. Granting of Use and Derivative Use Immunity

Under 18 U.S.C. §6002, the government can grant use-and-derivative-use immunity to a witness when he or she is required to testify in a federal criminal proceeding. This means that any statement made by the witness cannot be used against them, and any evidence derived from the witness’s statement cannot be used to prosecute them. When the witness’s Fifth Amendment privilege is waived under 18 U.S.C. §6002, this section preserves the government’s right to prosecute the witness if the witness commits perjury, makes a false statement, or fails to comply with the immunity order.

2. Waiving the Fifth Amendment Protection by Testifying

When a defendant testifies during a criminal trial, he or she effectively waives the Fifth Amendment protections of the U.S. Constitution. Defendants who testify during their witness examination open themselves up to questioning about the same subjects that they addressed in their direct testimony. While this is true for the subjects that they addressed during their direct testimony, defendants’ Fifth Amendment protections will still be available for topics that were not presented during their direct testimony.

Criminal Offenses That Can Be Charged Against a Witness

Regardless of their protection, if a witness provides a false statement during a criminal proceeding, he or she can be prosecuted for the federal offense of perjury under 18 U.S.C. §1621. Perjury is a felony offense that can result in up to five years’ imprisonment in federal prison. Perjury occurs when a witness “knowingly and willfully” makes a “materially false” statement during a proceeding while under oath.

Another potential criminal offense for a witness in a federal trial is making a false statement. Under 18 U.S.C. §1001, the government can prosecute anyone who knowingly makes a materially false, fictitious, or fraudulent statement in a federal matter.

A third potential criminal offense that witnesses must avoid during a trial is obstructing the administration of justice. Under 18 U.S.C. §1503, it is a crime to “corruptly, or by threats, or force, or by any other means, influence, obstruct or impede, or endeavor to influence, obstruct or impede the due administration of justice in any court of the United States.”

What Should I Do About Witness Contact or Threats?

Witnesses who testify in federal criminal cases often face various forms of threats and intimidation attempts. These threats can occur during the trial, and they can be real concerns that continue after the witness testifies. While there are various protections available for witness safety, witness preparation includes establishing safety protocol for the trial and after the witness testifies.

1. Witness Sequestration

Many times the judge will order witness sequestration. This means witnesses will not have access to other potential witnesses. If the judge issues a sequestration order, witnesses must follow all applicable rules. Witnesses should never discuss the case with other potential witnesses or any other person during the trial or trial recesses.

2. Reporting Threats or Harassment Attempts

If you receive threats, harassment, or intimidation attempts during the trial, save copies of the communication, including texts and emails, and promptly report them to your lawyer or law enforcement personnel. With the evidence in hand, a prosecutor can file a motion for a protective order, which may include additional witness protection and restrictions on the access to the witness.

If you are a cooperating witness in a federal case, the person who is targeting you is likely a defendant who has a pending federal case against him or her. If the individual who is targeting you is a defendant who was released on bail and is awaiting sentencing, then he or she has released conditions that he or she must abide by. If you report this to your lawyer, your lawyer will use the information to inform the prosecution team in the case, and the prosecution team will contact the judge. The judge may consider revocation of bail, among other measures, to ensure witness safety.

3. Witness Intimidation and Obstruction of Justice

The targeting of a witness, regardless of the communication’s nature, can constitute a federal criminal offense of witness intimidation under 18 U.S.C. §1512(b). Witnesses who testify against a co-defendant need to recognize when they are being targeted and when to report a potential crime to the government. If the government knows the witness is being targeted and you are not aware, then this may pose a risk that the information will not be used in court, which is contrary to the government’s interests.

Contact a Federal Criminal Defense Attorney

Nothing here is legal advice, and the details of your case matter. Todd Spodek and Spodek Law Group take federal criminal and white collar cases nationwide, from offices in New York, Brooklyn, Queens and Los Angeles. You can reach the firm at 212-300-5196.