The 22-year-old man accused of shooting U.S. Congresswoman Gabrielle Giffords of Arizona will appear in a federal court in Phoenix on Monday.
Jared Loughner faces one count of attempted assassination of a member of Congress, two counts of killing an employee of the federal government and two counts of attempting to kill a federal employee.
Meanwhile, U.S. President Barack Obama has called for a moment of silence Monday morning at 11 a.m. Washington time, to honor the victims. Flags at the White House and other public and military buildings also will be lowered to half-staff for the week.
Separately, House of Representatives Speaker John Boehner said that House votes scheduled for this week are postponed. Lawmakers are expected to honor the shooting victims on Wednesday.
Six people died in the mass shooting Saturday at a grocery store in Tucson, where Giffords, a Democrat, was meeting with constituents. The victims include a nine-year-old girl, a federal judge and a congressional staff member.
Medical authorities on Sunday said Giffords still is in critical condition, but they are "cautiously optimistic" about her recovery after being shot in the head.
Dr. Peter Rhee of Arizona's University Medical Center told reporters Giffords is in a medically induced coma as she begins to recover from surgery. But he said she has been following simple commands.
Police say a woman waiting in line to meet Giffords grabbed the ammunition clip out of Loughner's hand as he paused to reload the gun. Two other bystanders then tackled the gunman, who was apprehended at the scene.
Doctors said of the 14 people wounded, only Giffords remains in critical condition.
In several YouTube videos, a person who posted under the name Jared Loughner criticizes the government and calls for a new currency. Law enforcement officials say they are investigating the videos.
Last March, Giffords was one of at least 10 House Democrats harassed for their support of the U.S. health care reform legislation. The front door of her office in Tucson was shattered in an act of vandalism.
In November, Giffords was re-elected to a third term in the House of Representatives. She was first elected to Congress in 2006.