North Dakota U.S. Attorney Timothy Q. Purdon, center, and South Dakota U.S. Attorney Brendan V. Johnson, right, at the 2012 United Tribes Technical College Powwow in Bismarck, N.D. (Erin Hill-Oban)

They are known as “the Dakota Boys,” two federal prosecutors who have focused on improving law enforcement in tribal communities around the country.

Now, North Dakota U.S. Attorney Timothy Q. Purdon and South Dakota U.S. Attorney Brendan V. Johnson are stepping down and going into private practice together.

For more than four years, beginning in 2009, Purdon, 46, and Johnson, 39, took turns chairing a Justice Department panel focused on Native American issues. They both served on a committee that advised Attorney General Eric H. Holder Jr. on other criminal justice matters. Their departures add a degree of uncertainty to the future of efforts to improve public safety in Indian country.

The reservations in the Dakotas have suffered, as have the 566 Indian tribes in 35 states around the country, from a long history of neglect by the U.S. government, and they struggle with high rates of poverty, domestic violence, sexual assault and suicide.

Along with Native American tribes, Purdon shared criminal jurisdiction over four reservations, including one in the Bakken oil field, which is facing a crime wave fueled by a huge market for illegal drugs.

In an effort to better protect Native Americans living there, Purdon and his attorneys met routinely with tribal leaders, and his office increased its prosecution of crimes on reservations.

“Tim Purdon has been an outstanding United States Attorney, a fierce advocate for the people of North Dakota and a strong national leader whose efforts to improve public safety in Indian Country have made a profound difference — and touched countless lives,” Holder said in a statement.

Johnson, the son of former senator Tim Johnson of South Dakota, organized a trip for Holder and U.S. attorneys from around the country in 2011 to see Pine Ridge in South Dakota, a reservation that is ravaged by 87 percent unemployment and rotting and overcrowded public housing.

No attorney general had gone to Pine Ridge since Robert F. Kennedy did more than 50 years ago. At the time, Kennedy said he regretted not bringing flowers to lay at the sacred burial site at the Wounded Knee Memorial, according to Tracy Toulou, the director of the Justice Department’s Office of Tribal Justice and a descendant of the Colville Confederated Tribes in Washington state. When Johnson brought Holder to the Wounded Knee Memorial, Holder laid a wreath.

“It was a moment I will remember and I think everyone there will remember for the rest of their lives,” Toulou said.

In a statement, Holder called Johnson, who shares criminal jurisdiction with the tribes on nine reservations, “not only a respected champion for tribal justice in his own right, but a critical national leader — offering sound guidance, wise counsel, and candid advice on a host of pressing issues.”

In 2013, the Justice Department promoted a new law, the Violence Against Women Act, that had been passed by Congress to allow for the first time in 35 years the nation’s tribes to prosecute certain crimes of domestic violence committed by non-Indians on reservations.

The Justice Department “transformed a dysfunctional process that too often allowed domestic violence cases in Indian Country to languish and disappear, the sad result of a system in which the federal government and tribal officials would too rarely communicate, let alone collaborate,” Holder said.

Three tribes in 2014 began implementing the law, and in March, many more tribes will assert the new authority. More than 20 non-Indians have been charged so far by tribal prosecutors, and federal prosecutors have convicted more than 140 defendants under the law’s federal assault statutes.

“We haven’t solved the problems of crime and justice in Indian country,” Purdon said in an interview. “That will take decades. But the Obama administration has taken the first step.”

Richard S. Hartunian, the U.S. attorney for the Northern District of New York, said “the efforts of the Dakota Boys were a turning point in U.S.-tribal relations.”

“Brendan and Tim were the right leaders at the right time to carry out the vision of President Obama and Attorney General Holder to improve public safety in Indian country,” Hartunian said in an interview.

Heather Dawn Thompson, a member of the Cheyenne River Sioux tribe and a former assistant U.S. attorney who served under Johnson, said the next two U.S. attorneys in the Dakotas should be Indian prosecutors.

“With both Tim and Brendan leaving, it is concerning that momentum may be lost on the progress they have made,” Thompson said. “Indian country is hopeful that the Obama administration will appoint Native American candidates to fill both the South Dakota and North Dakota U.S. attorney vacancies and continue to build on these legacies.”