Criminal Justice Section  


Criminal Justice Magazine
Spring 2002
Volume 17 Issue 1

Trial Tactics

Stephen A. Saltzburg

Permissible, Impermissible Corroboration of Witnesses

Every lawyer who relies upon a key witness at trial looks for ways to corroborate the witness or to bolster the witness’s credibility. There are permissible and impermissible ways for lawyers to go about this task, however, and mistakes can lead to reversals on appeal and charges of unethical or unprofessional conduct. Thus, it is important for lawyers to know what they can and cannot do.

Generally, lawyers who do what the highest court in their jurisdiction tells them to do can rest easy that they are acting properly. But, there are appellate decisions that simply fly in the face of basic rules of evidence and that ought to be flagged as potentially dangerous before lawyers rely too much upon them and thereby get themselves into trouble. One of these decisions is United States v. Martinez, 253 F.3d 251 (6th Cir. 2001). As we shall see, the court properly found that the prosecutor erred in the questioning of a government witness, but it identified the wrong error and its mandate for the future, if followed, is certain to get lawyers on both sides of cases in trouble with trial courts and on the defensive with respect to their trial behavior.

The Martinez facts

Juan Antonio Martinez and Juan Armando Sauceda were charged with conspiracy to distribute marijuana. Sauceda was also charged with possession with the intent to distribute. The U.S. Drug Enforcement Administration (DEA) had focused attention on Sauceda as a seller of marijuana and attempted to set up a delivery of 400 pounds of marijuana to him. Two men—Juan Reyes and Ronald Carboni—met with Sauceda to discuss marijuana trafficking. Unbeknownst to Sauceda, Carboni was a government informant. Reyes and Carboni went to Sauceda’s hotel and offered Sauceda samples of marijuana. Sauceda declined to purchase any because of its poor quality. Reyes and Carboni left Sauceda and arranged for Martinez to deliver 315 pounds of marijuana to Reyes’s home.

Sauceda and Martinez were separately arrested, one at a hotel and the other at home. Police searched three storage units rented by Sauceda and found 282 pounds of marijuana. They searched Martinez’s home and found 47 pounds of marijuana.

Martinez and Sauceda were indicted along with four other codefendants.

Corroborating Carboni

The court of appeals described Carboni as the main government witness against Sauceda. (253 F.3d at 253.) It then focused on Sauceda’s complaint on appeal that the prosecutor improperly vouched for and bolstered Carboni’s testimony. Sauceda’s complaint focused on the following trial testimony by a narcotics deputy:

Q: Now, you’ve had the occasion to work with Mr. Carboni not only on this case but on some other cases?

A: Yes, Ma’am.

Q: Approximately how many?

A: Seven other cases.

Q: And what did you find about the information he had provided to you?

A: That the information he’s provided has always been credible, it’s been accurate and truthful.


The court’s opinion cited its earlier decision in United States v. Francis, 170 F.3d 546, 550 (6th Cir. 1999), as the governing law on improper vouching: "Improper vouching occurs when a prosecutor supports the credibility of a witness by indicating a personal belief in the witness’s credibility thereby placing the prestige of the office of the United States Attorney behind that witness," and "[i]mproper vouching involves either blunt comments or comments that imply that the prosecutor has special knowledge of facts not in front of the jury. . . ." Applying this test to the exchange between the prosecutor and the narcotics deputy, the court stated that "[h]ere, it is clear that the prosecutor did not engage in improper vouching because the prosecutor did not make any comments indicating that she had a personal belief in Carboni’s credibility." (253 F.3d at 254.)


Having rejected the claim that improper vouching occurred, the court turned to the claim of improper bolstering. Again it cited Francis for the governing standard: "Bolstering occurs when the prosecutor implies that the witness’s testimony is corroborated by evidence known to the government but not known to the jury." ( Id., citing 170 F.3d at 551.)

The court suggested that Francis prescribed the correct approach to corroborating a witness testimony and relied upon Francis for the proposition "that the prosecutor ‘may ask a government agent or other witnesses whether he was able to corroborate what he learned in the course of a criminal investigation,’" but, "if the prosecutor pursues this line of questioning, she must also draw out testimony explaining how the information was corroborated and where it originated." ( Id., citing 170 F.3d at 551.) The rule that the court drew from Francis was simply stated by the court: "If a prosecutor asks a government agent whether the agent was able to corroborate information provided by an informant, the prosecutor must introduce to the jury how that information was corroborated, e.g., via documents or searches." ( Id.)

Applying this test, the court was critical of the prosecutor and found that she engaged in improper bolstering:

In the case at bar, the prosecutor elicited testimony from narcotics deputy Glendening that in each of the seven prior cases where Carboni provided information to the police, the information had been corroborated. However, the prosecutor did not provide the jury with evidence of how, in those instances, the information was corroborated. It was precisely this type of omission that the Court in Francis deemed improper bolstering. Id. at 551 ("The prosecutor’s failure to introduce to the jury whether the information was corroborated via documents, searches, conversations, or other means would lead a reasonable jury to believe that the prosecutor was implying a guarantee of truthfulness based on facts outside the record."). Here, we find that the prosecutor engaged in improper bolstering.

(253 F.3d at 254.)

The court held that the improper bolstering, which amounted to one isolated event at trial, was not prejudicial, especially given the overwhelming evidence of guilt. And the prosecutor suffered no adverse consequences from the finding of error. But the fact remains that the court held that the prosecutor acted improperly. Although the court was correct in saying that the prosecutor erred, its reasoning is almost certainly incorrect and is likely to lead lawyers in other cases who attempt to do what the court said to violate the specific restrictions of Federal Rule of Evidence 608.

The Francis case

Before turning to the Federal Rules of Evidence and Rule 608, it is useful to examine the Francis decision upon which the Martinez court placed so much reliance. Francis involved a series of money laundering charges. One key government witness, Walker, was a drug dealer who had laundered drug money. Walker was arrested in Florida on an unrelated drug charge and decided to reveal the money laundering operation and to cooperate with the DEA. Walker testified for the government and was bolstered with the testimony of a federal agent in a way that the court found improper:

Here, the prosecutor asked Agent Blackwood repeatedly whether he had corroborated information obtained from Mr. Walker. There were at least fourteen such inquiries. Although Agent Blackwood answered each in the affirmative, he provided further detail in only two instances. He did this by properly adding that he had corroborated what Mr. Walker had told him by checking police reports, bank records, tax records, and interviews and conversations with other individuals. He also testified that he had corroborated the drug dealing by arranging for an undercover officer to purchase drugs. On all other occasions, however, Agent Blackwood responded to questions about corroboration by merely asserting that he had, in fact, corroborated the information. The prosecutor’s failure to introduce to the jury whether the information was corroborated via documents, searches, conversations, or other means, would lead a reasonable juror to believe that the prosecutor was implying a guarantee of truthfulness based on facts outside the record. This particular group of comments therefore amounts to improper bolstering.

(170 F.3d at 551.)

The difference in the cases

There is an important difference between Francis and Martinez that the court of appeals apparently missed. In Francis, it appears that Walker testified about his role in the money laundering, the way in which the laundering occurred, and other facts that supported the charges brought against the defendants. When Agent Blackwood was asked to testify with respect to corroboration, the prosecutor was attempting to prove that what Walker said was true. The truth of what Walker said was crucial because it related to the very charges brought against the defendants.

The problem in Francis was that the agent/witness did not demonstrate that he had personal knowledge that the facts related by Walker were true. Had the agent actually done an investigation that corroborated Walker’s facts, the agent could have testified to the results of the investigation. What he could not do was put his own credibility behind Walker’s by simply stating that he had corroborated Walker’s testimony without revealing how he had done so and to what extent specific facts were corroborated. In other words, to the extent the agent had relevant evidence regarding the defendant’s actions, it would both corroborate Walker and independently tend to prove guilt.

Martinez presented an entirely different set of facts. The deputy was not asked to corroborate Carboni’s testimony as to what Sauceda did in the case at bar. Instead, the prosecutor called the deputy to testify to Carboni’s reliability on other occasions involving other cases. This is a far cry from Francis, and it appears that the prosecutor was more correct in her approach to the deputy than was the court of appeals. The prosecutor did make a mistake, however, but not the mistake the court of appeals identified.

Federal Rule of Evidence 608

The rule that governs the prosecutor’s questioning of the deputy regarding Carboni is Rule 608. It reads in relevant part as follows:

Rule 608. Evidence of Character and Conduct of Witness

(a) Opinion and reputation evidence of character.—The credibility of a witness may be attacked or supported by evidence in the form of opinion or reputation, but subject to these limitations: (1) the evidence may refer only to character for truthfulness or untruthfulness, and (2) evidence of truthful character is admissible only after the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise.

(b) Specific instances of conduct.—Specific instances of the conduct of a witness, for the purpose of attacking or supporting the witness’ credibility, other than conviction of crime as provided in rule 609, may not be proved by extrinsic evidence. They may, however, in the discretion of the court, if probative of truthfulness or untruthfulness, be inquired into on cross-examination of the witness (1) concerning the witness’ character for truthfulness or untruthfulness, or (2) concerning the character for truthfulness or untruthfulness of another witness as to which character the witness being cross-examined has testified. . . .

Neither a prosecutor nor any other lawyer may seek to "support" the credibility of a witness until "the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise." It is difficult to tell from the opinion in Martinez whether Sauceda attacked Carboni’s character for truthfulness—e.g ., by a slashing cross-examination. If not, then the prosecutor erred in seeking to support the witness’s credibility. The error would not be for failing to introduce corroborative evidence; it would be for seeking to support credibility at all.

Assuming that Carboni’s character was attacked, Rule 608(a) makes clear that supporting evidence must be "in the form of opinion or reputation" and that specific acts are not permitted. Thus, the court of appeals’s criticism of the prosecutor for failing to offer evidence to prove that, on specific occasions that had nothing to do with the charges against Sauceda, Carboni was shown to be truthful is unwarranted. The prosecutor could not validly have sought to do what the court of appeals appeared to mandate, since to do so would be to violate Rule 608.

To be more specific, suppose that the narcotics deputy was examined in the manner that the court of appeals mandated and that defense counsel objected under Rule 608. The examination might look like this:

Prosecutor: Did Mr. Carboni identify any other wrongdoers in other cases?

Defense: Objection. Whether he did or not is irrelevant.

Prosecutor: Your Honor, the witness will testify that Mr. Carboni identified John Doe as a marijuana dealer, and we found John Doe with marijuana.

Defense: That has nothing to do with this case.

Prosecutor: It demonstrates the credibility of the witness.

Defense: You cannot support the credibility of the witness with specific acts. Rule 608 forbids it.

The court: Defense counsel is correct. The objection is sustained.

The end result will be the same whether the prosecutor is asking the narcotics deputy about drugs or about documents.

Prosecutor: Did Mr. Carboni identify any other wrongdoers in other cases?

Defense: Objection. Whether he did or not is irrelevant.

Prosecutor: Your Honor, the witness will testify that Mr. Carboni identified John Doe as the man who opened off shore bank accounts in an unrelated case, and we have a signature card from the bank with Doe’s signature on it.

Defense: That has nothing to do with this case.

Prosecutor: It demonstrates the credibility of the witness, and it does so with a document.

Defense: You cannot support the credibility of the witness with specific acts. Rule 608 forbids it.

The court: Defense counsel is correct. The objection is sustained.

In short, the court of appeals mandated that which no lawyer is permitted to do under Rule 608. Rule 608 has been unchanged in its limitation since its adoption in 1975. The danger in the Martinez holding is that it encourages improper behavior that might get lawyers who follow the case in trouble.

The prosecutor’s mistake

The prosecutor may well have known that Rule 608(b) prevented her from offering the corroborative evidence that the court of appeals found missing. Even so, she violated Rule 608 by the form of the questions asked. She could have asked the narcotics deputy how long he had known Carboni, whether he had an opinion as to Carboni’s character for truthfulness, and whether he was familiar with Carboni’s reputation for truthfulness. Answers to all of these questions would comply with Rule 608. This was not, however, the form of the examination that took place.

Instead, the prosecutor asked the narcotics deputy how many times he had worked with Carboni and asked about the specific occasions. This may sound a little like opinion evidence but it actually is evidence about specific acts and is not permissible. The following example illustrates what would have been permissible.

Prosecutor: How long have you known Mr. Carboni?

Witness: About five years.

Prosecutor: What was the general nature of your relationship with Mr. Carboni?

Witness: He assisted us as an undercover informant in several cases.

Prosecutor: As a result of your relationship with Mr. Carboni, do you have an opinion as to his character for truthfulness?

Witness: Yes, I do.

Prosecutor: What is that opinion.

Witness: My opinion is that he is a truthful man.

Prosecutor: Have you heard others in the community speak of Mr. Carboni’s character for truthfulness?

Witness: Yes, I have.

Prosecutor: What is Mr. Carboni’s reputation for truthfulness in the community?

Witness: It is the same as my opinion; he has the reputation of a truthful man?

All of these questions are permissible, provided that Carboni’s character for truthfulness was attacked. Whether the prosecutor could go a little further and ask, "Is there anything in your dealings with Mr. Carboni that ever caused you to doubt his truthfulness?" likely would turn on whether the trial judge viewed this as consistent with opinion testimony or as moving too close to specific acts.


By comparing Francis and Martinez and recognizing how they are different, lawyers can avoid the mistake made by the court of appeals in its criticism of the prosecutor and the actual mistake that the prosecutor made in examining the narcotics deputy. The following principles emerge from the cases and are consistent with Rule 608(b).

1. One witness with relevant testimony about the disputed facts in a case may testify consistently with another witness. Thus, the federal agent in Francis would have been free to testify about the facts he learned in his investigation of the defendants for the crimes charged. As long as the agent had personal knowledge and his testimony did not violate any other rule of evidence, such as the hearsay rule, the agent’s investigative facts were independently relevant to prove the prosecution’s case. That the agent’s testimony also corroborated a key witness is another benefit for the government, a permissible one. Consistency among witnesses is a legitimate form of corroboration.

2. A witness who is called to testify about another witness’s actions in an unrelated case is not offering testimony that is relevant to the case being tried. Such a witness is properly treated as a character witness.

3. A witness may have (a) relevant testimony about the case being tried and (b) also may seek to testify about another witness’s actions in an unrelated case. As long as the witness is offering testimony that falls within (a), the testimony is admissible; but when the witness shifts to testify about (b), Rule 608 comes into play.

4. One witness may not be called to testify in support of another witness’s credibility until the other witness’s character for truthfulness has been attacked. Rule 608(a) specifically states that this is the rule.

5. Once a witness’s credibility for truthfulness has been attacked, the party relying on the witness may call a character witness to support the attacked witness. The character witness is limited to testifying in the form of reputation and opinion evidence, not as to specific acts.

6. None of these rules will matter much unless the party who objects to the testimony of a supporting witness raises the correct objection.


Stephen A. Saltzburg is the Howrey Professor of Trial Advocacy, Litigation, and Professional Responsibility at George Washington University School of Law in Washington, D.C. He is also a contributing editor to Criminal Justice magazine and a Section delegate to the ABA House of Delegates.


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