The U.S. Supreme Court should give a Texas man found guilty of a 2005 double homicide and abandoned by his attorney a "fair shot" at challenging his conviction by resolving a disagreement among federal circuit courts, the American Bar Association told the justices.

In a Monday amicus brief, the ABA urged the high court to take up the petition for certiorari from Joseph Gamboa, who alleges his appointed habeas lawyer barely met with him and conducted one day of legal research before filing a "sham petition" to challenge the constitutionality of Gamboa's murder convictions and death sentence.

The Fifth Circuit stands alone in prohibiting prisoners whose attorneys have abandoned them from reopening habeas proceedings to challenge their convictions on constitutional grounds, the ABA said. The Second, Seventh and Ninth circuits recognize that a provision in the Federal Rules of Civil Procedure, known as Rule 60(b), gives abandoned prisoners an avenue to reopen the proceedings, according to the brief.

The rule may be a death row inmate's last chance "to correct a grave error before execution," the ABA said, and prisoners in the Fifth Circuit do not have this option.

"In capital cases, this entrenched conflict means that a petitioner's life may ride not on the merits of his habeas claims, but on the forum in which they are filed," the ABA said.

The high-stakes nature of death penalty cases spurred the ABA to adopt its own guidelines for attorneys representing clients who face capital punishment. The guidelines lay out lawyers' duties to investigate all aspects of the case, litigate all "arguably meritorious" issues, maintain close contact with the client regarding the litigation, and form an appropriate defense team, the brief said.

Gamboa's case, the ABA said, "strikes at the heart of that effort."

A jury convicted Gamboa of capital murder in 2007 for the killings of two men during a robbery at a San Antonio bar — murders Gamboa "steadfastly denies committing," the petition for certiorari said. After an unsuccessful effort to challenge his conviction through the state habeas process, Gamboa said he sought to file a federal habeas petition in 2015.

But Gamboa alleges his attorney abandoned substantive work on his case "almost immediately after" he was appointed. Following a year of extensions and "virtually no work on the case," Gamboa's counsel turned over a generic habeas petition that was copied and pasted from that of another client, Gamboa said. And in response to the state of Texas' answer to the petition, Gamboa's attorney conceded in a two-paragraph reply filing that the claims in the petition were foreclosed, Gamboa said.

The federal court denied Gamboa's habeas petition, and later refused his motion to reopen the proceedings and denied him a certificate of appealability, the petition said. The Fifth Circuit affirmed the ruling and declined to review the case en banc.

The ABA said on Monday that Gamboa's allegations, if true, constitute abandonment and not merely negligent representation.

"Although abandoning a client is serious misconduct in any context, it is even more serious in criminal cases in general, and capital cases in particular, where the potential for harm to the client is immense," the ABA said.

Gamboa's attorney before the Supreme Court, Stephen Ferrell, told Law360 in a Tuesday email that the legal team appreciates the ABA's support "in highlighting the critical issue of attorney abandonment in capital habeas cases." It is imperative that the high court take up the case to "ensure fairness and justice in our legal system," he said.

A spokesperson for Texas Department of Criminal Justice said the department does not comment on pending litigation.

The ABA is represented by its own Deborah Enix-Ross and by Derek C. Reinbold, Kathleen W. Hickey and Jordan R.G. González of Kellogg Hansen Todd Figel & Frederick PLLC.

Gamboa is represented by John P. Elwood, Andrew T. Tutt, Sean A. Mirski, Dana Or, Jack Hoover, William T. Sharon, Nicole L. Masiello and Jacob P. Saracino of Arnold & Porter and by Stephen Ferrell, Susanne Bales and Emily Elison of Federal Defender Services of Eastern Tennessee Inc.

Bobby Lumpkin, director of the Correctional Institutions Division of the Texas Department of Criminal Justice, is represented by Ali M. Nasser of the Texas Office of the Attorney General.

The case is Joseph Gamboa v. Bobby Lumpkin, Director, Texas Department of Criminal Justice, Correctional Institutions Division, case number 23-323, in the Supreme Court of the United States.

--Editing by Jill Coffey.