Caballero v. Miller: Reinforcing the Prejudice Requirement for Ineffective Assistance of Counsel under AEDPA

Introduction

This commentary examines the Second Circuit’s April 2, 2025 decision in Caballero v. Miller, which establishes a rigorous standard for demonstrating prejudice in ineffective-assistance-of-counsel claims on federal habeas review under the Antiterrorism and Effective Death Penalty Act of 1996 (AEDPA). The petitioner, Andrew Caballero, was convicted in New York state court for the 1995 rooftop murder of Jason Kollman. He asserted that his trial counsel, Robert DiDio, and appellate counsel, Danielle Muscatello, provided constitutionally deficient representation by failing to investigate alternative-suspect leads—particularly involving Michael Lugo—and by not raising those failures on direct appeal. The district court granted habeas relief, but the Second Circuit reversed, emphasizing that under Strickland v. Washington and AEDPA’s deferential standard, a habeas petitioner must proffer admissible evidence of what uninvestigated witnesses would have testified to and show a reasonable probability of a different outcome.

Summary of the Judgment

The Court reversed the district court’s grant of habeas relief under 28 U.S.C. § 2254.
It held that the state court’s denial of relief did not unreasonably apply the Strickland standard because Caballero failed to present evidence of what a proper investigation would have yielded or how it would have changed the verdict.
The Court further concluded that appellate counsel could not be deemed ineffective for failing to raise an issue on direct appeal that depended on evidence outside the trial record.

Analysis

Precedents Cited

Strickland v. Washington (466 U.S. 668 (1984)): Established the two-prong test for ineffective assistance—(1) deficient performance and (2) prejudice.
Harrington v. Richter (562 U.S. 86 (2011)): Emphasized the double deference when § 2254(d) and Strickland both apply.
Knowles v. Mirzayance (556 U.S. 111 (2009)): Clarified that a state court’s reasonable Strickland determination is upheld unless it is objectively unreasonable.
Cullen v. Pinholster (563 U.S. 170 (2011)): Held that to show prejudice, a habeas petitioner must demonstrate a substantial likelihood of a different outcome even under AEDPA deference.
Lindstadt v. Keane (239 F.3d 191 (2d Cir. 2001)) and Schulz v. Marshal (345 F. App’x 627 (2d Cir. 2009)): Illustrate successful claims where post-trial evidence identified critical witnesses whose uncalled testimony would have undermined the prosecution’s case.
Pierotti v. Walsh (834 F.3d 171 (2d Cir. 2016)): Recognizes New York’s rule that ineffective-assistance claims reliant on evidence outside the record must be raised in collateral proceedings, not on direct appeal.

Legal Reasoning

The Court applied AEDPA’s standard: a federal court may grant habeas relief only if the state court’s adjudication was “contrary to, or involved an unreasonable application of, clearly established Federal law” (28 U.S.C. § 2254(d)(1)). Under Strickland, prejudice requires a “reasonable probability” that, but for counsel’s errors, the outcome would have been different.

The petition rested on trial counsel’s alleged failure to investigate Rosario disclosures revealing alternative-suspect information (especially about Lugo) and appellate counsel’s failure to raise that claim on direct appeal. The Second Circuit held:

Although DiDio’s pretrial investigation was limited, Caballero did not produce any testimony or affidavits from the uninvestigated witnesses to show what helpful evidence they would have provided or that they would even have testified.
The Rosario materials themselves contained largely hearsay or second-hand suspicions regarding Lugo, while direct statements tied Caballero to the scene. Nothing in the record indicated that additional investigation would have uncovered admissible testimony more favorable than what DiDio already used to impeach prosecution witnesses.
Under AEDPA and Strickland’s double deference, the state court reasonably concluded there was no “substantial” likelihood of a different verdict even if counsel had conducted a fuller investigation.
Appellate counsel’s failure to raise the trial counsel claim on direct appeal was likewise not unreasonable: New York law requires collateral proceedings for ineffective-assistance claims that depend on evidence outside the trial record. Moreover, even if the claim had been properly raised, Caballero could not show a reasonable probability of success without evidence of prejudice.

Impact

This decision reinforces several key principles:

Under AEDPA’s § 2254(d), habeas petitioners face a high bar in proving ineffective assistance. It is insufficient to point to counsel’s failure to investigate; petitioners must affirmatively show what that investigation would have produced and how it would have changed the outcome.
“Double deference”—to both the state court’s Strickland application and to counsel’s strategic choices—means federal courts will rarely second-guess a state court’s factual or mixed factual-legal determinations absent clear error.
In New York, claims of ineffective assistance that rely on evidence beyond the trial record must proceed through collateral review (§ 440.10), not direct appeal. This decision upholds that procedural requirement and clarifies appellate counsel’s duties under Strickland in that context.
Practitioners should ensure that pretrial counsel conducts a thorough investigation and that any lapses are documented with evidentiary support for collateral challenges.

Complex Concepts Simplified

AEDPA Deference: Federal courts may grant habeas relief only if the state court’s decision was not just incorrect, but unreasonably so under Supreme Court precedents.
Strickland’s Two-Prong Test:
1. Performance: Counsel’s conduct must fall below an objective standard of reasonableness.
2. Prejudice: There must be a reasonable probability that, without the errors, the result would have been different.
Rosario Material: Under New York law, the prosecution must disclose prior witness statements so the defense can use them to impeach witness credibility.
Collateral vs. Direct Appeal: In New York, claims that depend on evidence not in the trial record cannot be raised on direct appeal but must be litigated in a post-conviction (collateral) proceeding.

Conclusion

Caballero v. Miller underscores the rigorous prejudice requirement for ineffective assistance claims in federal habeas proceedings under AEDPA. Petitioners must present concrete, admissible evidence showing what uninvestigated leads or witnesses would have contributed and a substantial likelihood that the outcome would have differed. The decision also reaffirms New York’s framework requiring collateral review for claims that hinge on evidence outside the record and clarifies that appellate counsel is not deficient for foregoing issues that cannot succeed without extra-record proof of prejudice. Together, these principles fortify the high threshold for federal habeas relief and guide criminal defense strategy both at trial and on appeal.