On Tuesday, the Supreme Court handed down two important criminal procedure decisions, both allowing defendants to seek habeas corpus review of their convictions in federal court. The 5-to-4 majority, with Justice Anthony Kennedy joining the court’s four moderate liberals, reached the right result in each case. But, in a larger sense, the two decisions show how much the scope of habeas review has been curtailed by the Supreme Court in the last three decades, so that it now must work around earlier precedents to avoid doing injustice.

In a case from Texas, Trevino v. Thaler, the court ruled that a death-row inmate in Texas can make the claim of ineffective counsel for the first time in a federal habeas petition because the rules of Texas procedure made it virtually impossible for him to raise that issue during an appeal in state court.

Carlos Trevino was convicted of murder and sentenced to death by a Texas trial court. His trial lawyer did not present evidence of his childhood abuse or cognitive impairment at the sentencing phase. The United States Court of Appeals for the Fifth Circuit ruled that since he did not raise the ineffective assistance of counsel issue in his state appeal, he could not raise it in a federal habeas petition.

Writing for the majority, Justice Stephen Breyer noted “the importance of federal habeas corpus principles designed to prevent federal courts from interfering with a state’s application” of its own procedural rules. But the federal appeals court ruling “would create significant unfairness,” he said, in any system like Texas’ that “does not offer most defendants a meaningful opportunity to present a claim of ineffective assistance of trial counsel” in an appeal.

In a case from Michigan, McQuiggin v. Perkins, the court ruled correctly that an inmate who can make a credible showing of actual innocence is not barred from filing a habeas petition to have his case reviewed by a federal court — even if the petition is filed after the one-year limit for such claims under the Antiterrorism and Effective Death Penalty Act of 1996, the federal statute that sets forth rules about habeas use.

The federal statute says a state prisoner ordinarily has a year to file a federal habeas petition after the conviction becomes final or after he should have discovered the new evidence that he claims supports his innocence. Floyd Perkins, convicted of murder and sentenced to life without parole, filed his petition six years after he received new evidence. He relied on three affidavits from witnesses that pointed to another man who had been with Mr. Perkins and the victim around the time of the murder.

Justice Ruth Bader Ginsburg, writing for the majority, said that the “miscarriage of justice” exception allows a federal court to consider a habeas petition despite the one-year limit and that a credible claim of innocence meets the high standard for that exception.

The Michigan and Texas cases show how heavily engaged the court has gotten in the regulation of criminal justice. Even when the court does the right thing, as it did in these two cases, it often appears to be finding exceptions to harsh rules that it created or upheld in earlier cases. In the Texas case, the court further tinkered with “the machinery of death,” to use Justice Harry Blackmun’s phrase, rather than doing what it should have done by now: shut down the machinery by abolishing the death penalty.