Federal prosecutors will not seek the death penalty against a Wyoming teenager accused of killing a couple who authorities said stopped to help him on the Crow Indian Reservation in Montana, the U.S. Justice Department announced Friday.

Attorney General Loretta Lynch decided against seeking capital punishment in the case of Jesus Deniz Mendoza after consulting with federal prosecutors in Montana, the agency said in a one-sentence statement.

Justice Department spokeswoman Melissa Hornbein declined to give a reason for Lynch's decision. The agency's recommendation process for death penalty cases is confidential, she said.

Mendoza's defense attorneys have said their client suffers from significant mental illness.

One of Mendoza's court-appointed attorneys, Anthony Gallagher, said he was "very pleased" with the government's decision.

"Mr. Mendoza still is maintaining his not guilty plea and we will move forward in the process," said Gallagher, with the federal defender's office.

Mendoza, 18, of Worland, Wyoming, faces 12 charges including two counts of first-degree murder in the July deaths of Jason and Tana Shane near Pryor.

Authorities say the couple and their daughter were shot after stopping to help Mendoza along a roadway. The daughter survived.

Mendoza could face life in prison if convicted.

Montana U.S. Attorney Mike Cotter met with members of the Shane family to tell them about the death penalty decision before it was publicly announced, Hornbein said.

Prosecutors earlier this year sought a court order that would have allowed them to conduct a competency examination on Mendoza to see if he was fit for trial. But his defense team objected, and U.S. District Judge Susan Watters turned down the request.

Defense attorneys reserved the right to ask for such an exam in the future.