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(CNN) -- U.S. District Judge John Roll was one of six people killed Saturday in a shooting at an Arizona supermarket, authorities said.

President Barack Obama confirmed Roll's death in a public statement hours after the shooting, saying Roll had served the legal system for nearly 40 years.

In addition to the six dead, 12 others -- including U.S. Rep. Gabrielle Giffords -- were wounded when a gunman opened fire outside a grocery store in Tucson, where the congresswoman was holding a constituent meeting, police said.

A native of Pennsylvania, Roll was a federal judge for the U.S. District Court for the District of Arizona. He began his career as a bailiff in Pima County Superior Court and rose to be chief judge for the District of Arizona, a position he held since 2006.

"Unfortunately, he was in the wrong place at the wrong time," Pima County Sheriff Clarence Dupnik said about Roll, describing him as sincere, fair-minded and brilliant.

Roll was nominated by former President George H. W. Bush and joined the court in 1991.

He was recommended for the position by U.S. Sen. John McCain, R-Arizona, who released a statement soon after the attack.

"Words are inadequate to express such a profound loss to his family, friends, state and country, but it is appropriate to note that a man of great qualities and character was struck down today, and the wickedness of this atrocity, which included the murder of a small child, has broken the hearts of many and will be mourned for years to come," said McCain.

Two years ago, Roll received death threats after ruling that a $32 million civil-rights lawsuit could proceed. The lawsuit was filed by illegal immigrants against a rancher in the state.

His ruling led to public outrage from radio talk show hosts and others, and eventually led to threats.

Roll was placed under protection by federal marshals for several weeks, though no charges were ever filed related to the threats.

Roll also received criticism recently when he asked to delay bringing felons to trial in Tucson, citing a judicial emergency. He said in a November letter to the 9th U.S. Circuit Court of Appeals that the ever-increasing number of federal felony arrests had overwhelmed his court.

"The addition of what sometimes seems to be an inexhaustible number of law enforcement agents and federal prosecutors in Tucson division has now produced a tsunami of federal felony cases far beyond the management capacity of the four active district judges in Tucson division," he wrote.

Roll had also been assigned to hear the ethnic studies ban case out of Tucson, according to the lead attorney on the case, Richard Martinez. The case involves a new law banning certain ethnic studies programs in public schools.

Vice President Joe Biden released a statement soon after the shooting in which he praised Roll and called for prayers.

"Chief Judge John Roll was a dedicated jurist whose death is a terrible loss to Arizona and to the country," said Biden.

"We do not yet know the motivation behind these shootings. But what we do know is that there is simply no justification, no rationale for such senseless and appalling violence in our society."

Chief Justice of the United States John Roberts similarly praised his colleague and called Roll's death a tragic loss.

"Chief Judge John Roll was a wise jurist who selflessly served Arizona and the nation with great distinction, as attorney and judge, for more than 35 years," said Roberts. "(His) death is a somber reminder of the importance of the rule of law and the sacrifices of those who work to secure it."

Roll was a father of three and a grandfather of five, the U.S. DIstrict Court for the Arizona district said.

CNN's Bill Mears contributed to this report.