Burke said, "This case also involves potential death-penalty charges, and Department rules require us to pursue a deliberate and thorough process. [Wednesday]'s charges are just the beginning of our legal action. We are working diligently to ensure that our investigation is thorough and that justice is done for the victims and their families."
According to the indictment, Loughner, 22, attempted to assassinate Gabrielle Giffords, a member of Congress, and attempted to murder two federal employees, Ron Barber and Pamela Simon.
A conviction for attempted assassination of member of Congress carries a maximum penalty of life in prison, a $250,000 fine or both, according to Burke's office.
Loughner himself is set to be back in court next week. A preliminary hearing Monday for Loughner has been moved to a larger federal courtroom in Phoenix. The courtroom is the centerpiece of the downtown Phoenix courthouse and is mostly used for ceremonial and high-profile hearings.
Six people were killed and 13 wounded in the Jan. 8 attack at a grocery store. Giffords was shot in the head and remains in serious condition.
In the days since the shooting, numerous bits of information have emerged that paint a portrait of Loughner as a disturbed man who alienated most of those around him. His relationship with his father has been described by people who knew the family as strained.
On the morning of the shooting, Loughner was seen running into the desert as his father chased after him - a scene that took place after his father saw him removing a mysterious black bag from the family's car. According to authorities, Loughner purchased ammunition that morning and was later pulled over for running a red light.
Giffords will be moved Friday to a rehabilitation hospital in Houston to begin the next phase of her recovery from a gunshot wound, barring medical issues that would delay the transfer, her family said Wednesday.