Andrew Luger, who as U.S. attorney prosecuted the nation's largest terrorism recruitment case and helped solve the 27-year-old mystery of Jacob Wetterling's disappearance, was one of 46 remaining U.S. attorneys appointed by President Barack Obama asked to resign Friday.

Luger confirmed in a written statement that he delivered his resignation, effective immediately. "Serving the people of Minnesota as their United States Attorney has been the most fulfilling and rewarding experience of my professional life," he said. "The office that I am leaving this evening is comprised of the most talented and motivated professionals I have ever known."

Sarah Isgur Flores, a Justice Department spokeswoman, said Attorney General Jeff Sessions asked all remaining holdover U.S. attorneys to resign "in order to ensure a uniform transition."

The request shocked many in the Minnesota legal community. A law enforcement official said state and federal authorities had lobbied for Luger to keep his position. Luger spent Thursday evening at a community meeting on countering extremism and was to provide an update next week at the St. Paul Jewish Community Center on hate crime investigations.

U.S. Sen. Amy Klobuchar said she will campaign for Luger to be renominated and has already spoken to Sessions and his deputy attorney general about Luger's work. "His professionalism is so much bigger than any partisan decision," she said.

She said she will argue for maintaining consistency at an office that has led terrorism investigations, a major sex-trafficking ring prosecution and the investigation into Prince's April 2016 death.

U.S. Sen. Al Franken called Luger "a dedicated public servant who has served the people of Minnesota with distinction" and also vowed to "strongly urge the new administration to renominate him to this post."

Luger was nominated for the position in November 2013, confirmed by the U.S. Senate and sworn into office in February 2014.

It is not uncommon for new administrations to request the resignations of U.S. attorneys appointed by presidents from opposing parties. But the George W. Bush administration eased U.S. attorneys out gradually while officials sought replacements, as did Obama's Justice Department.

The scale of Friday's request was unexpected, said Thomas Heffelfinger, who twice served as U.S. attorney in Minnesota. Heffelfinger — and Sessions — were among 93 U.S. attorneys asked to resign in 1993 after President Bill Clinton took office. Heffelfinger said he was surprised Sessions made a similar request Friday, given his past experience.

"It caused a lot of problems within the Department of Justice having most of the U.S. attorneys being interims," he said. "This is not good."

First Assistant U.S. Attorney Greg Brooker is expected to fill Luger's position on an interim basis. Luger's departure creates a fourth key federal vacancy in Minnesota, joining two open judgeships and U.S. marshal.

Legal experts said Luger's exit will have swift effects.

Minneapolis attorney William Mauzy said he expects a quieter period from the office during the transition. "I doubt that someone there on a temporary basis, in a period of turmoil, will be particularly aggressive, but instead keep their head below the firing line," he said.

Steve Schleicher, a former assistant U.S. attorney, helped lead the prosecution of Wetterling's killer, Danny Heinrich. The case was the product of a special prosecutions unit Luger created.

"What he did was create an atmosphere where we could take a case like that and work it as hard as we needed to resolve it," Schleicher said. "When we got closer to resolving the case, Andy was an instrumental part of the team."

Jon Hopeman, a veteran Minneapolis lawyer who was assistant U.S. attorney from 1983 to 1994, applauded Luger's work on trying to prevent extremism after being confronted with an unexpected surge in terrorism recruitment cases soon after he took office. "I count him among the most successful people ever to hold that office," Hopeman said.

In 2015 and last year, Luger charged 11 young Twin Cities men — including two in absentia — with plotting to join the Islamic State in Iraq and Syria (ISIS). The prosecutions coincided with his office's management of one of three federal pilot projects aimed at curbing terrorism recruitment that targeted local Somali-Americans.

Luger will leave office with at least one major case unresolved: the federal investigation into how rock icon Prince obtained the illicit fentanyl responsible for his overdose death last year. The U.S. Drug Enforcement Administration turned the investigation over to Luger's office this year for a decision on prosecution, said a source familiar with the case. Authorities are looking into the source of counterfeit painkiller pills that Prince had.

Luger's office also indicted 17 people behind a sex trafficking ring that sprawled from Thailand to the Twin Cities. The case, charged last fall, is pending trial.

In a phone interview Friday, Richard Thornton, special agent in charge of the FBI's Minneapolis division, called Luger "far and away" the best U.S. attorney with whom he has worked through three decades in law enforcement. Thornton said both the ISIS recruitment and Wetterling cases would not have had the same outcomes without Luger at the helm. Luger led marathon strategy sessions to reach an agreement with both the defense and Wetterling's family in the days leading up to the discovery of Jacob's remains last year, Thornton said.

Jacob's mother, Patty, said the Wetterlings are "sad to see him go. He played a critical role in bringing Jacob home."

Thornton confirmed that support for Luger ran deep in the federal law enforcement community. "Andy did the job, in my opinion, in a very nonpolitical manner," he said. "If you just walked in and looked at his record, you had probably no idea where he was on the political spectrum."

Staff writer Randy Furst contributed to this report.

Stephen Montemayor • 612-673-1755 Twitter: @smontemayor