State v. Rivas, 2017 NMSC 22

On July 29, 2011, 15‑year‑old Juan Rivas broke into and murdered 83‑year‑old Clara Alvarez; he was arrested and two recorded police interviews were used at trial.
August 1 interview: occurred before a delinquency petition was filed; Rivas (15) signed a juvenile advice‑of‑rights form and gave a detailed confession.
August 2 petition filed; on August 3 the children’s court appointed a public defender and a guardian ad litem.
August 6 interview: detectives, after contact from Rivas’s father, questioned Rivas in juvenile detention without counsel present; Rivas again signed the advice form and gave a statement that shifted blame toward others.
Trial: both recorded interviews were admitted; jury convicted Rivas of first‑degree murder and related counts and sentenced him to life. Rivas appealed, arguing (1) ineffective assistance for failure to suppress the August 1 statement, and (2) the district court erred in denying suppression of the August 6 statement. The Supreme Court of New Mexico affirmed.

Issue	State's Argument	Rivas's Argument	Held
Validity of waiver and counsel‑related suppression for Aug. 1 (pre‑petition)	Waiver was knowing, intelligent, voluntary; statements admissible	Waiver invalid under Children’s Code and constitution; counsel ineffective for not moving to suppress	Waiver valid under totality of circumstances; no prima facie ineffective‑assistance because a suppression motion would not have succeeded
Right to counsel and suppression for Aug. 6 (post‑petition)	Waiver again valid; motion untimely but merits preserved; statements admissible	Sixth Amendment and Children’s Code protections attach after filing; juvenile cannot validly waive counsel outside counsel’s presence	Sixth Amendment right attached and, for juveniles, is indelible for interrogation; statements obtained without counsel should have been suppressed (district court erred)
Timeliness of suppression motion	Motion was untimely under Rule 5‑212; State argued prejudice and gamesmanship	Rivas argued merits and ineffective assistance excuse late filing	Court reviewed merits despite untimeliness; majority considered timeliness but reached merits; concurrence would dispose on untimeliness alone
Prejudice / Harmless‑error from admission of Aug. 6 statement	Any error was harmless beyond a reasonable doubt	Admission was harmful and required reversal	Error in admitting Aug. 6 statement was harmless; no reasonable possibility it contributed to convictions

Miranda v. Arizona, 384 U.S. 436 (establishes Miranda warnings and waiver principles)
Moran v. Burbine, 475 U.S. 412 (waiver must be free, deliberate, and with full awareness)
Massiah v. United States, 377 U.S. 201 (Sixth Amendment right to counsel after initiation of adversary proceedings)
Montejo v. Louisiana, 556 U.S. 778 (Miranda warnings can bear on Sixth Amendment waiver issues)
J.D.B. v. North Carolina, 564 U.S. 261 (children experience custodial interrogation differently)
In re Gault, 387 U.S. 1 (juveniles require special procedural safeguards and counsel protections)
Sullivan v. Louisiana, 508 U.S. 275 (standard for harmless‑beyond‑a‑reasonable‑doubt review)