People v. Mack

Larry Mack sought leave in the circuit court of Cook County to file a successive postconviction petition, claiming trial counsel was ineffective for failing to investigate and argue that the victim's shooting was accidental, and that his life sentence was void. The circuit court denied leave, finding the claim barred by res judicata and that Mack failed to satisfy the cause-and-prejudice test required under the Post-Conviction Hearing Act for successive petitions. Mack appealed to the Illinois Appellate Court, First District.

The appellate court affirmed, holding that Mack's ineffective assistance claim had already been raised and rejected across multiple prior proceedings—his 1984 direct appeal, his 1990 postconviction petition, and successive petitions in 2013 and 2022—making the claim barred by res judicata. Because Mack did not argue cause in his brief, and could not do so given this extensive litigation history, he failed to meet the threshold required to overcome the bar. The court also rejected Mack's reliance on the Illinois Supreme Court's decision in People v. Guy, 2025 IL 129967, distinguishing it as a case where the underlying claim had never been previously adjudicated and where the supreme court exercised unique supervisory authority after the State forfeited procedural defenses. Guy did not announce an intervening change in law and created no mechanism for the appellate court to bypass the Act's statutory bars.

For practitioners, this decision reinforces that repeated postconviction filings raising substantively identical claims will be barred by res judicata absent a genuine showing of cause and prejudice, and that Guy's narrow, fact-specific exception should not be read broadly to excuse procedural defaults in ordinary successive petition cases.