Opinion by Judge SILVERMAN; Concurrence and Dissent by Judge NOONAN.

Petitioner Kelly DePetris shot and killed her husband Dana DePetris while he was asleep in bed. At trial, she claimed “imperfect self-defense” — that is, she claimed to have had an actual, honest belief that she was in imminent danger even if such a belief was objectively unreasonable. Under California law, imperfect self-defense *1059 is not a complete defense to homicide; however, if established, it negates malice and reduces murder to voluntary manslaughter.

To prove her claim that she acted out of an actual fear that her husband would make good on his threats to kill her and their baby that night, petitioner attempted (1) to offer into evidence Dana’s handwritten journal and (2) to testify herself about how having read the journal contributed to her belief that Dana’s threats were to be taken seriously. The journal contained Dana’s chilling account of his violent behavior toward his first wife and others. The trial court excluded as irrelevant the journal and petitioner’s testimony about having read it. 1 Although the California Court of Appeal held that the journal and related testimony were indeed admissible, it held that their exclusion was harmless because the jury had heard other evidence relating to Dana’s propensity for domestic violence.

We hold, first, that given the subjective element of imperfect self-defense, the .erroneous exclusion of this evidence was not mere evidentiary error. It unconstitutionally interfered with petitioner’s due process right to defend against the charges. We also hold that this error very likely had a substantial and injurious effect on the verdict. Petitioner’s credibility and state of mind were the central issues in the case. Because of the subjective aspect of imperfect self-defense, the trial court’s erroneous preclusion of both the journal and especially petitioner’s own testimony about having read it — to explain why she did what she did — was a crucial ruling. None of the other evidence adduced at trial could in any way make up for Kelly DePe-tris’s own testimony about her state of mind, or for Dana DePetris’s handwritten corroboration of it. We reverse.

I. Background

We take the following recitation of facts from the opinion of the California Court of Appeal in which petitioner Kelly DePetris is referred to as “appellant”:

The prosecution moved in limine to exclude from evidence Dana DePetris’s journal and any reference to it. The journal contained Dana’s own handwritten description of his physical abuse of his homosexual companion, his beating of his stepdaughter, his rape of a friend’s girlfriend, and numerous accounts of his beating of his first wife, including the breaking of her eardrum. The prosecution also sought to preclude petitioner’s own testimony about *1061 having read the journal both before and during the marriage, and to its effect on her. In addition, the prosecution sought to exclude the portion of petitioner’s videotaped police interview in which, in the course of trying to explain her actions on the morning of the shooting, she mentioned the journal and its effect on her; the prosecution intended to introduce incriminating portions of the tape, but sought to exclude any reference to the journal. Finally, the prosecution sought to limit the testimony of Dr. Nancy Kaser-Boyd, an expert on Battered Woman’s Syndrome, to prohibit her from mentioning the journal. The motion in limine was granted. The journal and all references to it were ruled inadmissible.

Petitioner was found guilty of first degree murder with use of a firearm. She was sentenced to twenty-nine years to life in prison. The California Court of Appeal affirmed, holding unanimously that the journal evidence was admissible, but also holding (with one justice dissenting) that the error was not prejudicial in light of other evidence that went to the jury to prove petitioner’s credibility and the victim’s propensity for violence.

The district court denied habeas relief, holding that the excluded evidence was but “one piece of physical evidence” that was not critical to the defense. Assuming ar-guendo that constitutional error had occurred, the court held that such error was harmless in light of other evidence that was adduced in support of her theory of defense.

II. Jurisdiction and Standard of Review

We have jurisdiction pursuant to 28 U.S.C. § 2258 .

A district court’s decision to grant or deny a petition for writ of habeas corpus is reviewed de novo. Bribiesca v. Galaza, 215 F.3d 1015, 1018 (9th Cir.2000). Under the Antiterrorism and Effective Death Penalty Act of 1996, we grant habeas relief only when the state court decision was “contrary to, or involved an unreasonable application of, clearly established Federal law, as determined by the Supreme Court of the United States.” 28 U.S.C. § 2254 (d)(1); Williams v. Taylor, 529 U.S. 362 , 120 S.Ct. 1495 , 146 L.Ed.2d 389 (2000). “When analyzing a claim that there has been an unreasonable application of federal law, we must first consider whether the state court erred; only after we have made that determination may we then consider whether any error involved an unreasonable application of controlling law within the meaning of § 2254(d).” Van Tran v. Lindsey, 212 F.3d 1143, 1155 (9th Cir.), cert. denied, — U.S. -, 121 S.Ct. 340 , 148 L.Ed.2d 274 (2000). The latter step is a review for clear error. 2

Further, we apply the Brecht standard to determine whether a constitutional error was harmless. Habeas relief is warranted only if the error had a “substantial and injurious effect or influence in determining the jury’s verdict.” Brecht v. Abrahamson, 507 U.S. 619, 638 , 113 S.Ct. 1710 , 123 L.Ed.2d 353 (1993); Bains v. Cambra, 204 F.3d 964, 977-78 (9th Cir.) cert. denied, — U.S. -, 121 S.Ct. 627 , 148 L.Ed.2d 536 (2000).

III. Analysis

There is no denying that the precluded journal was admissible as a matter of California evidence law. The California Court of Appeal so found and that finding is binding on us. See Franklin v. Henry, *1062 122 F.3d 1270, 1273 (9th Cir.1997). The questions then become whether the erroneous exclusion was contrary to or an unreasonable application of clearly established Federal law as determined by the Supreme Court of the United States, and if so, whether the error was also “objectively unreasonable.” If the error was “objectively unreasonable,” we then inquire whether it had a substantial and injurious effect on the jury’s verdict.

A. Was a constitutional right violated?

“The right of an accused in a criminal trial to due process is, in essence, the right to a fair opportunity to defend against the State’s accusations.” Chambers v. Mississippi 410 U.S. 284, 294 , 93 S.Ct. 1038 , 35 L.Ed.2d 297 (1973); accord Davis v. Alaska, 415 U.S. 308, 317 , 94 S.Ct. 1105 , 39 L.Ed.2d 347 (1974), Washington v. Texas, 388 U.S. 14, 19 , 87 S.Ct. 1920 , 18 L.Ed.2d 1019 (1967). The Supreme Court has made clear that the erroneous exclusion of critical, corroborative defense evidence may violate both the Fifth Amendment due process right to a fair trial and the Sixth Amendment right to present a defense. Chambers, 410 U.S. at 294 , 93 S.Ct. 1038 ; Washington, 388 U.S. at 18-19 , 87 S.Ct. 1920 .

For example, in Washington , the defendant was charged with murder. He admitted being present at the time the victim was shot, but denied shooting him and testified that he tried to persuade the actual shooter — Fuller—to leave the scene before the shooting. The trial court permitted Washington to testify on his own behalf but precluded him from calling Fuller as a corroborating witness. The Supreme Court held that exclusion of this corroborative evidence was unconstitutional even though the defendant himself was allowed to testify. Washington, 388 U.S. at 15-17, 22 , 87 S.Ct. 1920 . The Court stated that the right to offer such evidence “is in plain terms the right to present a defense, the right to present the defendant’s version of the facts as well as the prosecution’s to the jury so it may decide where the truth lies.” Id. at 19 , 87 S.Ct. 1920 .

Likewise, in Chambers the trial court allowed an eyewitness to testify that he saw someone named McDonald kill the victim, but precluded the defendant from corroborating that testimony with evidence that McDonald had confessed. As it did in Washington , the Supreme Court held that exclusion of this critical corroborative evidence was not only erroneous but unconstitutional because it interfered with the defendant’s right to defend himself against the state’s accusation. Chambers, 410 U.S. at 298-302 , 93 S.Ct. 1038 .

Along the same lines, in Franklin v. Henry, 122 F.3d 1270, 1273 (9th Cir.1997), we held that where a defendant’s guilt hinges largely on the testimony of a prosecution’s witness, the erroneous exclusion of evidence critical to assessing the credibility of that witness violates the Constitution.

As these cases illustrate, the trial court’s exclusion of Dana DePetris’s journal and petitioner’s testimony about having read it was not mere evidentiary error. It was of constitutional dimension. The ruling went to the heart of the defense. Petitioner’s sole defense was that she killed her husband in an honest belief that she needed to do so to save her life. The success of the defense depended almost entirely on the jury’s believing petitioner’s testimony about her state of mind at the time of the shooting. As the prosecutor argued in closing argument, to “accept the position of the defense, you must accept what [petitioner] has said to you in this trial. * * * [T]o find voluntary manslaughter, you have to find that [petitioner] is being honest with you.” There is simply no denying that the most important witness in the defense of Kelly DePetris was Kelly DePetris herself. The trial court not only excluded the journal, which would have corroborated petitioner’s testimony, but worse still, it prevented petitioner from testifying fully in her own behalf about why she did what she did— this in a case where proof of the defen *1063 dant’s state of mind was an essential element of the defense.

With all due respect, the district court’s ruling that the erroneous exclusion of the journal evidence was not of constitutional magnitude reveals a misunderstanding of its true significance. The district court characterized the trial court’s ruling as the exclusion of only “one piece of physical evidence.” In describing the trial court’s ruling that way, the district court failed to take into account that the overriding significance of the proffered evidence was not so much the journal itself as petitioner’s own testimony about how having read the journal influenced her assessment of the danger she perceived. It also must be remembered that the trial judge excluded not only the journal, but also petitioner’s trial testimony about it, and the portion of the videotape of the police interrogation where petitioner mentions it, and any reference to it by the expert on Battered Woman’s Syndrome. It was not just “one piece of physical evidence” that was excluded.

The trial court precluded petitioner from testifying fully about her state of mind and from presenting evidence that would have corroborated her testimony. Because this evidence was critical to her ability to defend against the charge, we hold that the exclusion of this evidence violated petitioner’s clearly established constitutional right to due process of law— the right to present a valid defense as established by the Supreme Court in Chambers and Washington . Further, based on the foregoing independent review of the record, we find that the state court’s error was also objectively unreasonable. See Delgado v. Lewis, 223 F.3d 976, 981-82 (9th Cir.2000).

B. Did the error have a substantial and injurious effect on the verdict?

The petitioner has shown that the erroneous exclusion of the journal evidence likely had a substantial and injurious effect on the verdict, as required by Brecht , for the following reasons:

First, petitioner’s state of mind was the critical issue at trial. The case would rise or fall on whether the jury would believe that petitioner acted in actual fear of imminent harm from her husband when she shot him, yet petitioner was prevented from testifying fully about why she feared him so. It is no answer to say that the record contained other evidence of the husband’s violence. Her state of mind was uniquely within her knowledge, and as California Court of Appeal Justice Swager wrote in dissent,

People v. DePetris, No. A071092, slip op. at 18 (Cal.App.Ct. Nov. 20, 1996)(emphasis added).

Second, proof of petitioner’s credibility was crucial to her defense. As already noted, the prosecutor’s closing argument dramatically underscored the importance of petitioner’s credibility. The prosecutor strenuously argued that the only way the jury could acquit petitioner of murder and convict her of manslaughter was if it somehow believed her claim of actual fear. To establish imperfect self defense, it was absolutely essential that petitioner prove her credibility. The journal was powerfully and indisputably probative of this point. The journal corroborated — in Dana DePe-tris’s own handwriting — petitioner’s testimony that her fear had a genuine basis in fact.

Third, although it is true that the jury heard testimony from other people about the husband’s violence, this other testimony came from witnesses aligned with the petitioner — her parents, half-sister, and a friend. “[T]he excluded evidence, unlike the evidence [from petitioner’s family and *1064 friends] was not subject to attack on the grounds of bias or self-interest. It was the only unbiased source of corroboration for [petitioner’s] testimony.” People v. DePetris, No. A071092, slip op. at 20 (Cal.App.Ct. Nov. 20, 1996) (Swager, J., dissenting). Indeed, it was from the victim himself.

United States v. James, 169 F.3d 1210 (9th Cir.1999), is instructive on the critical importance of corroboration in a self-defense case. In James , the defendant’s only defense to homicide was that she believed herself to be in danger of grievous bodily harm or death from the victim. Essential to her defense was her knowledge of, and belief in, the decedent’s bizarre accounts of previous acts of vicious violence he had committed. These stories were so atrocious that one might doubt that someone would really tell them of himself. The trial judge excluded court and police records that would have corroborated the defendant’s testimony that she had heard the decedent tell her those things and, therefore, that she had reason to be afraid of him. On appeal, Judge Noonan wrote for our en banc court:

169 F.3d at 1214-15 .

Such is the case here.

The dissent argues that the exclusion of the corroboration was harmless because “[t]here was no testimony of a fear of imminent peril to be corroborated.” Dissent at 1198. That is not correct. Petitioner testified that before they went to bed, Dana threatened to kill her and her son if she did not have the rent in the morning. He awakened in the middle of the night and again told her that she was “clocking out” if she didn’t come up with the rent. In the morning, awakened by the dog, Dana ordered her to get her “fuck ass” out of the bed and let the dog out. He then told her that he would “take care of [her] later.” She testified that as she stood in the bedroom moments later, after letting out the dog, just before the shooting, she thought to herself, “It’s the only way out. It’s him or me.” This testimony was evidence of her fear of imminent harm. The excluded journal evidence would have corroborated her testimony about why she believed that harm was imminent and that shooting him provided the only avenue of escape. Although the unreasonableness of that belief disqualifies the petitioner from ordinary self-defense, the actuality of that belief, if true, entitles her to imperfect self-defense.

As recently explained by the California Court of Appeal in People v. McCoy, petition for review granted, 98 Cal.Rptr.2d 430 , 4 P.3d 264 (Cal.2000):

Id. (internal citations omitted).

IY. CONCLUSION

We hold that the erroneous exclusion of both the journal evidence and any reference to it — especially petitioner’s own testimony about it — unconstitutionally interfered with her ability to defend against the charges against her. The preclusion of this highly probative evidence went to the crux of the case, and the harm caused by its exclusion was not cured by the receipt of other evidence that was significantly less compelling. Petitioner has shown that her trial was substantially and injuriously affected by the erroneous ruling, and therefore, the writ of habeas corpus should have been granted. We REVERSE AND REMAND for further proceedings consistent with this opinion.

. Petitioner also sought to introduce the portion of her videotaped police interrogation where she told detectives about the journal. She also attempted to introduce testimony about the journal by an expert on Battered Woman's Syndrome.

. In Van Tran , we explained the standard set forth in Williams :

Van Tran, 212 F.3d at 1153-54 .