Trevino v. Davis, 138 S. Ct. 1793

Carlos Trevino was convicted of capital murder in Texas; at penalty phase the State presented his criminal history and gang membership, and mitigation consisted only of testimony from his aunt about family hardship and his caring nature.
Trevino later raised an ineffective-assistance-of-trial-counsel claim, arguing counsel failed to investigate and present evidence of fetal alcohol spectrum disorder (FASD) and related developmental deficits as mitigation.
Postconviction experts and lay witnesses produced substantial new mitigating evidence: FASD diagnoses, low-average intellectual functioning, developmental delays, prenatal alcohol exposure, childhood abuse/neglect, poor academic and daily‑living skills; other witnesses described violent episodes and gang-related conduct.
The Fifth Circuit reviewed prejudice de novo and held the new evidence was a “double‑edged” sword (mitigating and aggravating) and affirmed denial of habeas relief, concluding Trevino could not show a reasonable probability of a different sentence.
The U.S. Supreme Court denied certiorari; Justice Sotomayor (joined by Justice Ginsburg) dissented, arguing the Fifth Circuit misapplied Strickland and failed to reweigh the totality of mitigating and aggravating evidence as required by precedent.

Issue	Plaintiff's Argument	Defendant's Argument	Held
Whether trial counsel’s failure to investigate/present FASD mitigation prejudiced Trevino under Strickland	Trevino: new FASD evidence, considered with trial evidence, would likely have led at least one juror to vote for life	State: new evidence was double‑edged — it showed violent tendencies and an expert said FASD did not impair moral culpability, so it would not change the outcome	Fifth Circuit: affirmed denial of habeas relief, finding no reasonable probability of different sentence; Supreme Court denied certiorari (dissent argues Fifth Circuit erred)
Proper method for assessing prejudice when new evidence includes both mitigating and aggravating aspects	Trevino: courts must reweigh the totality of mitigation and aggravation as a jury would, not dismiss mitigation because some evidence is adverse	State: emphasis on the aggravating aspects makes mitigation insufficient to overcome death verdict	Dissent (Sotomayor): Fifth Circuit misapplied precedents (Wiggins/Williams/Rompilla/Wong) by isolating adverse aspects rather than holistic reweighing; certiorari denied so no correction by Court

Strickland v. Washington, 466 U.S. 668 (establishes deficient performance and prejudice test for counsel claims)
Wiggins v. Smith, 539 U.S. 510 (courts must reweigh totality of mitigation and aggravation when assessing prejudice)
Williams v. Taylor, 529 U.S. 362 (mitigating evidence that also contains adverse facts must be evaluated in context and may affect moral culpability)
Rompilla v. Beard, 545 U.S. 374 (failure to investigate mitigation including cognitive impairment can establish prejudice even if new evidence has adverse aspects)
Wong v. Belmontes, 558 U.S. 15 (assessing prejudice requires weighing all new mitigating and aggravating evidence together)
Martinez v. Ryan, 566 U.S. 1 (narrow rule permitting federal habeas review of ineffective-assistance-of-trial-counsel claims where initial-review collateral counsel was absent or ineffective)
Trevino v. Thaler, 569 U.S. 413 (applies Martinez to Texas and remands for consideration of ineffective‑assistance‑of‑trial‑counsel claims)