Neither the notice nor the U.S. attorney's statement explains the decision. U.S. Attorney Amanda Marshall said the process leading to it was confidential.
The accused are 32-year-old David "Joey" Pedersen and his girlfriend, 28-year-old Holly Ann Grigsby. A federal grand jury indicted the pair in August 2012. They face trial in July on federal kidnapping, carjacking and murder charges.
They are charged with killing two men, one on the Oregon coast and another in Northern California, in what authorities called a white-supremacist scheme.
Pedersen and Grigsby have white-supremacist ties, and Pedersen has said in court that his motivation for the slayings was partly because of the victims' ethnicities or skin color. Pedersen said he believed the Oregon teenager was Jewish, and that he and Grigsby targeted the man in California because he was black.
Pedersen has pleaded guilty in state court to aggravated murder for the slaying of his father and stepmother in Everett, Wash., and has been sentenced to life in prison.
Grigsby's two lawyers did not immediately return calls for comment. Pedersen is representing himself.
Both defendants remain in federal custody, said Gerri Badden, spokeswoman for the U.S. Attorney's Office in Portland.
The death penalty has been used sparingly by the current administration, though it has not been eliminated, said Richard Dieter, executive director of the Washington, D.C.-based Death Penalty Information Center. On average, only about one case a year has been sought during the Obama administration, Dieter said.
Since the federal death penalty was reinstated in 1988, various attorneys general have approved seeking the death penalty in 492 cases. But only 70 of those cases have resulted in death sentences. And just three of those people have been executed, partly because of a hold on executions due to lethal-injection problems.
Death-penalty cases are rare, Dieter said, because they're hard to win, time-consuming and expensive.
"It's not only about the horrendousness of the crime, but about how strong the case is for guilt and how strong is the mitigating evidence that might convince a jury not to give the death penalty," Dieter said. "You need a very strong case, otherwise it's not worth going through the long, costly pursuit."
Mitigating evidence might include mental-health issues or even having multiple defendants with different circumstances, Dieter said, adding he wasn't commenting specifically on the Pedersen-Grigsby case.
Just last month, Holder announced that the federal government would seek a death sentence for the Boston Marathon terror bombing suspect Dzhokhar Tsarnaev if he is convicted.