A federal grand jury in Arizona indicted Jared Lee Loughner on Wednesday on charges of attempting to assassinate Democratic Representative Gabrielle Giffords and the attempted murder of two of her staff members.

Loughner, 22, is accused of opening fire on Giffords and a crowd of bystanders outside a grocery store on January 8, killing six people, including a federal judge, and wounding 13 others. He is expected to face additional federal and state charges.

Authorities have said Giffords, who remains hospitalized with a bullet wound to the head, was the gunman's primary target.

Today'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, U.S. Attorney Dennis K. Burke said in a statement.

The indictment did not include any murder charges for two other federal employees who were slain -- Judge John Roll, the chief federal judge in Arizona who had stopped at the supermarket store to talk to Giffords, or Gabe Zimmerman, the lawmaker's director of community outreach.

A five-county criminal complaint filed the day after the shooting included two first-degree murder charges for the deaths of Roll and Zimmerman. But an indictment frees the government from the need to present its case to a judge in a preliminary hearing in order to proceed to trial.

Loughner, who is being held in a medium-security prison north of Phoenix, is due to next appear in court on Monday, according to Burke's office.

The initial charges in the indictment against Loughner carry a maximum penalty of life in prison. But if he is indicted later for murder and convicted, he could face the death penalty.

The shooting spree has sparked a national debate about whether stricter gun-control measures should be adopted, including a renewed ban on high-capacity ammunition clips, and whether vitriolic political discourse was encouraging violence against politicians.

Loughner had ammunition clips that held nearly three dozen bullets, whereas traditional clips hold far fewer, according to law enforcement officials.

During the congressional debate last year over healthcare reform legislation, several lawmakers received death threats, and prosecutors filed charges in several cases.

Despite suffering a gunshot wound to the head at point-blank range, Giffords' doctors have described her survival as nothing short of a miracle. She is in serious condition at Tucson's University Medical Center.

Her congressional office issued a statement on Wednesday saying she is expected to be moved from the hospital to a rehabilitation facility in Houston on Friday, so long as her health allows.

Giffords to be discharged:

U.S. Rep Gabrielle Giffords is expected to be discharged from a Tucson hospital on Friday, two weeks after she was shot through the head, to begin in-patient rehabilitation at a facility in Texas, her office said on Wednesday.

After considering numerous rehab centers around the country, the congresswoman's family opted to move her to the TIRR Memorial Hermann Rehabilitation Hospital in Houston, citing its relative proximity to her hometown of Tucson and its reputation as a top-flight facility.

Giffords' husband, astronaut and space shuttle commander Mark Kelly, also has family in Houston and he pointed to Memorial Hermann's national reputation for treating serious penetrating brain injuries.

Memorial Hermann has been ranked as one of the top five rehabilitation hospitals in the United States for the past 21 years by U.S. News & World Report magazine.

Her transfer is anticipated for Friday, but because this is a fluid situation, the exact day of the move will depend on the congresswoman's health, her office said in a statement.

Giffords, 40, remains in serious condition at Tucson's University Medical Center. Her neurosurgeon has deemed her recovery thus far miraculous.

Dr. Michael Lemole, who operated on Giffords the day of the shooting, said Monday that her transfer from the hospital to rehabilitation will be the lawmaker's next milestone.

That's her graduation, Lemole said.

Giffords was shot on January 8 when a gunman opened fire on a crowd of constituents gathered to meet her outside a Tucson supermarket. Six bystanders including a federal judge and a 9-year-old girl were killed and 13 others were wounded, Giffords among them.

A 22-year-old college dropout, Jared Lee Loughner, who authorities described as mentally unstable, is charged with the shooting.

Giffords' medical condition was upgraded on Sunday from critical to serious after doctors removed a breathing tube that ran from a ventilator down her throat. They replaced it with a tracheotomy tube inserted through her neck and directly into her windpipe.

The tracheotomy and a feeding tube prevent her from speaking, and doctors described her over the weekend as largely incommunicative. But close relatives insist she is aware of her surroundings and socially interactive.

Giffords unfastened her husband's tie and unbuttoned the top button of his shirt after he had attended a memorial service for one of the other shooting victims, and she has begun reading cards sent by elementary school children, CNN reported Wednesday, citing an email from Giffords' mother to family and friends.