OPINION ON APPELLANT’S PETITION FOR DISCRETIONARY REVIEW
MEYERS, Judge,
delivered the opinion of the Court
in which McCORMICK, Presiding Judge, and KELLER, HOLLAND and WOMACK, Judges, joined.
Appellant was convicted by a jury on two counts of tampering with government documents. The Fourth Court of Appeals affirmed Appellant’s conviction. Carpenter v. State, 952 S.W.2d 1 (Tex.App.— San Antonio pet. granted). We granted Appellant’s petition for discretionary review to address whether the Court of Appeals erred in holding Appellant was properly precluded from cross-examining State’s witness Rudy Pete Rodrigues regarding federal conspiracy charges then pending against him.
Appellant argues that evidence of the pending federal charges was admissible under this Court’s decision in Carroll v. State, 916 S.W.2d 494 (Tex.Crim.App.1996). In Can-oil, this Court stated that “[a] defendant is permitted to elicit any fact from a witness intended to demonstrate that witness’ vulnerable relationship with the State.” Carroll, 916 S.W.2d at 500 (citing Alford v. United States, 282 U.S. 687, 692, 51 S.Ct. 218, 75 L.Ed. 624 (1931) and Harris v. State, 642 S.W.2d 471, 480 (Tex.Crim.App.1982)). Relying on that language from CarroU, Appellant posits that the pending federal charges demonstrated Rodrigues’ vulnerable relationship with the State and thus cross-examination was improperly limited. We disagree.
Exposing a witness’ motivation to testify for or against the accused or the State is a proper and important purpose of cross-examination. Parties are allowed great latitude to show “any fact which would or might tend to establish ill feeling, bias, motive and animus on the part of the witness.” London v. State, 739 S.W.2d 842, 846 (Tex.Crim.App.1987). The existence of pending federal charges may be relevant to establish bias or motive, as a federal defendant’s “substantial assistance” in a state prosecution may result in a downward departure from the United States sentencing guidelines. See United States Sentencing Guidelines § 5kl.l 18 U.S.C.A. The trial judge, however, has some discretion. Hurd v. State, 725 S.W.2d 249 (Tex.Crim.App.1987); Miller v. State, 741 S.W.2d 382, 389 (Tex.Crim.App.1987), cert. denied 486 U.S. 1061, 108 S.Ct. 2835, 100 L.Ed.2d 935 (1988). A trial judge may limit cross-examination as inappropriate for a number of reasons. Carroll, 916 S.W.2d at 498 (citing Delaware v. Van Arsdall, 475 U.S. 673, 679, 106 S.Ct. 1431, 89 L.Ed.2d 674 (1986) (for example, trial judge may exercise discretion to prevent harassment, prejudice, confusion of the issues, and marginally relevant interrogation)).
In order to impeach a witness with evidence of pending criminal actions, the proponent of the evidence must establish that the evidence is relevant. Carroll, 916 S.W.2d at 494; London, 739 S.W.2d at 846-48. Appellant wished to introduce evidence that, at the time of trial, the witness in question had been charged with theft in federal court (18 U.S.C. 666) and conspiracy to possess and distribute controlled substances, in an attempt to show bias or prejudice towards the State due to a “vulnerable relationship.” For the evidence to be admissible, the proponent must establish some causal connection or logical relationship between the pending charges and the witness’ “vulnerable relationship” or potential bias or prejudice for the State, or testimony at trial. See, e.g., McDuff v. State, 939 S.W.2d 607, 618 (Tex.Crim.App.1997) (permissible to show serious pending state charges against accomplice witness because such situation might have affected his testimony as a witness for the State; but impermissible to “elicit the accomplice witness’s knowledge or lack of knowledge of the difference in parole eligibility minimum time periods” because it “would not have any further shown his vulnerable relationship with the State or his potential motive, bias or interest”).
Appellant has not established a causal connection or logical relationship between the pending federal charges and the witness’ testimony at trial. Appellant does not argue, and the record does not demonstrate, why prosecution by the federal government for theft and conspiracy to possess and distribute controlled substances would tend to show that the witness’ testimony in this unrelated state prosecution for tampering with government documents might be biased. Appellant asserts that “[i]t is possible the witness believed his testimony in this case would be of some benefit,” but does not provide evidence to support her assertion. Indeed, even the testimony in support of Appellant’s bill of exception does no more than establish the factual basis of the pending federal charges. In addition, the federal charges pending at the time of trial arose after the witness seized the evidence that forms the basis of this case, and after the witness provided pretrial testimony. Appellant was free to use this pre-trial testimony to impeach the witness if it was inconsistent with his testimony at trial. Appellant did not show that the witness gave inconsistent testimony. The record shows that Rodrigues, a lieutenant with the Maverick County Sheriffs Department and a certified peace officer, testified regarding the process of seizing the documents with which Appellant was accused of tampering. Appellant has simply not provided any indication that the pending federal charges were relevant to potential bias or prejudice. Accordingly, we hold that the Court of Appeals’ determination that “there was danger that allowing such cross-examination would confuse the jury, or tempt it to use the facts developed in an improper way” is sound.
The judgment of the Court of Appeals is affirmed.
MANSFIELD, J., joins the opinion of the Court and files a concurring opinion.
PRICE, J., files a concurring opinion.
BAIRD, J., files a dissenting opinion in which OVERSTREET, J., joins.
. While Appellant's ground for review is couched in terms of reviewing the trial court’s evidentiary ruling, we note that the Court of Criminal Appeals is not an appellate court but a discretionary review court. We granted this petition to address an important point of law left unsettled by our opinion in Carroll v. State, 916 S.W.2d 494 (Tex.Crim.App.1996).
. The charges in question were later dropped. Carpenter, at 5 n. 2.
. In Carroll, four judges determined that the defendant should have been allowed to question a witness regarding then-pending state charges. Concurring, Judge Meyers, joined by Judge White, stated that the cross-examination should not be limited if the charges have been instituted by the same prosecuting authority:
In this case the charges pending against the State's witness originated in the same jurisdiction and were brought by the identical authorities as those for which the appellant stands accused. I therefore agree with the decision of our lead opinion to allow the defendant to use these charges for impeachment on cross-exam-¡nation of this witness. However, in future contexts, should these charges emanate from another jurisdiction or authority, I would hold that release of the information to the jury is subject to a discretionary ruling of the trial court under Rule 403 of the Texas Rules of Criminal Evidence. With these additional comments, I join the opinion of the Court.
The majority opinion did not address charges pending under a different prosecuting authority.
.We emphasize that the proponent is not required to establish actual bias. What is required is that the proponent make a showing of the witness' potential for bias. Naked allegations which do no more than establish the fact that unrelated federal charges are pending do not, in and of themselves, show a potential for bias.
. The testimony does not show, for example, the existence of a piea bargain agreement or negotiations, or show the witness’ belief regarding the existence or non-existence of any kind of "deal.” We note, however, that there are other ways to support the assertion that the witness believed testimony in this case would favorably affect the outcome of pending federal charges. It also fails to establish any connection between the state and federal charges.
. Rodrigues described the layout of the court building offices; the execution of the consent to search form, which he signed as a witness; the bathroom where the box was discovered; the process of photographing the box after it was discovered; the chain of custody of the box after it was seized; and the reports made in connection with the seizure.
.The Court of Appeals pointed out that the danger of jury confusion “was perfectly illustrated at oral argument, when Carpenter’s counsel argued that since the federal charges implicated Rodri-gues’ conduct as a peace officer, the charges were relevant to cast doubt on Rodrigues’ other actions as a peace officer.” Carpenter, at 5. Appellant could not have used the pending charges to impeach Rodrigues’ credibility because there was no final conviction. See Tex.R.-Evid. 609 (substantively identical to former Tex. R.Crim Evid. 609).