To read more on this story, see CNN affiliates KVOA and KGUN. Also, read a grand jury's indictment of suspect Jared Lee Loughner.
Tucson, Arizona (CNN) -- Arizona Rep. Gabrielle Giffords was able to stand with assistance on Wednesday, an aide said, with her doctor adding that the congresswoman has the strength to stand on her own.
"Today we were getting her out of bed again and we were able to stand with assistance," said Dr. Peter Rhee, Tucson's University Medical Center's trauma chief. "She's got the strength to stand on her own, lift her head up and these ... I see improvements every single day."
Rhee was speaking to CNN affiliate KVOA.
Giffords' chief of staff, Pia Carusone, told CNN Wednesday that Giffords had stood Wednesday "with assistance."
A federal grand jury in Tucson indicted Jared Lee Loughner on three charges of attempted murder on Wednesday.
Loughner, 22, was charged with attempting to kill Giffords and two of her aides, Ron Barber and Pamela Simon.
"We are in the early stages of this ongoing investigation," said U.S. Attorney Dennis K. Burke in a statement about the charges.
"This case also involves potential death-penalty charges, and (Justice) Department rules require us to pursue a deliberate and thorough process," the statement went on. "Today's charges are just the beginning of our legal action."
Federal law requires the U.S. to bring charges against of a defendant within 30 days of his or her arrests.
Legal experts said that more federal charges against Loughner are likely.
"This is really a placeholder indictment," CNN senior legal analyst Jeffrey Toobin said Wednesday. "The grand jury investigation will continue, there's a long way to go in these case and these charges will be there but I'm certain there will be more as well."
In addition to standing on Wednesday, Giffords' doctor said she was put in a chair and was able to look out a window.
"We went to a window and so she could see the mountains of Tucson," Rhee said. "There's no doubt in my mind that lifted up her spirits."
The congresswoman, who will be moved to a rehabilitation center in Texas later this week, had worries about her safety long before she was critically wounded by a gunman at a public event this month, her husband said on Tuesday.
"We've discussed it a number of times," Mark Kelly told KVOA. "She felt that that was a possibility, pretty much exactly what had happened ... there have been threats against her and other members of Congress."
Giffords was hosting a constituents' meeting outside a supermarket in Tucson when a gunman opened fire. Six people, including a federal judge and a 9-year-old girl, were killed and 13 others wounded.
Giffords was shot in the head. In an e-mail sent to friends and family members Tuesday and obtained by CNN, Giffords' mother, Gloria, writes that she will be moved from Tucson's University Medical Center to rehabilitation facilities in Houston on Friday.
"There is a team of medical specialists involved ... including military surgeons who specialize in bullet wounds to the head," the e-mail says. "They want to start aggressive rehab immediately."
Giffords' office confirmed the move and said that while the move is expected to be Friday, "the exact day of the move will depend on the congresswoman's health." Her family chose TIRR Memorial Hermann rehabilitation hospital in Houston, part of the Texas Medical Center, because of its reputation, one of her doctors said.
"The congresswoman's family wants to ensure she receives the best rehabilitative care possible for her type of serious penetrating brain injury," said Dr. Michael Lemole.
Kelly said that Memorial Hermann's proximity to Tucson was another factor in the decision.
"I am extremely hopeful at the signs of recovery that my wife has made since the shooting," he said. "The team of doctors and nurses at UMC has stabilized her to the point of being ready to move to the rehabilitation phase. Their goal -- and our goal -- has been to provide Gabby with the best care possible."
Loughner is next set to appear in court on Monday in Phoenix. Richard Kastigar, chief investigator for the Pima County Sheriff's Department, said Wednesday authorities believe he showed his gun to a friend before the shooting, "between Christmas and New Year's." After the shooting, the friend told his father about the exchange, and the father contacted police, he said. He would not name the friend.
Police have said Loughner bought the gun in November after passing a background check, and bought ammunition at a Walmart near his home hours before the shooting. Seven boxes of ammunition were found after the rampage in a black bag discovered in a dry river bed in Loughner's neighborhood.
In addition, authorities said Wednesday that the gunman apparently fired 32 shots, one more than previously thought. A woman found a bullet casing in her purse several days later, Kastigar said.
"A woman who was around the shooting scene that day found the casing and reported it to police," he said. "It fits right into our investigation. We always knew Loughner had one round in his chamber and 31 in the magazine."
Kastigar said he didn't know whether the woman attended the event at the Safeway, was a passerby or was coming out of the store at the time of the shooting.
Gloria Giffords writes that her daughter shows improvement every day "and shows higher levels of comprehension and complex actions.
"Yesterday, when Mark came back from speaking at her aide's memorial service, she reached up and untied his tie and undid the top button to his shirt," according to the e-mail.
"Last night, she took his iPod and scrolled through all the pictures. Early this morning she began to read cards made for her by some 4th graders! Her unbandaged eye tracked the lines, she opened the cards and turned them over reading the back. Mark's gotten pages of large print of Harry Potter's 1st book for her to hold and read."
The e-mail also says that Giffords gave her husband "a 20-minute neck and back rub."
Giffords remains in serious condition. A second, unnamed victim is listed in good condition.
Kelly told the affiliate the couple had been concerned about heated and divisive political debates, but despite the fears, Giffords' passion for public service was a priority.
"She was doing what she loved, she was representing the people of southern Arizona," Kelly said. "She felt it was very important for them to have the opportunity to walk up to her and tell her what they think."
Kelly said the lawmaker will resume her public service "stronger than ever" as soon as she's well enough. He predicted she would return to the scene of the shooting.
"She loves southern Arizona more than anything," he told CNN affiliate KGUN. "She's here every week, doing stuff like 'Congress on your Corner,' and I'm sure the first thing she's gonna do, when she's ready, is a 'Congress on your Corner' at that Safeway" where the shooting occurred.
The outpouring of support has been tremendous, Kelly said, including an elementary school student who sent his $2.85 in lunch money to Giffords with a card.
"I sealed it back up, and we're gonna give it back to him," Kelly said. "It almost made me cry just standing there in the room, just to see the kid put his lunch money in the envelope for her."'
Gloria Giffords wrote in the e-mail that her daughter has hard work ahead of her. She has been moving her limbs on command, according to the e-mail, and doctors have had her sitting up in a chair.
"So now comes the 'true grit' part," she wrote, "and (it) won't be a stroll in a park although Mark predicts she'll be up and walking around in 2 weeks. The physical and emotional therapy will proceed side by side and it'll be stringent."
Giffords has not been able to speak because of a breathing tube in her throat. Her mother wrote that Giffords will continue communicating more as she becomes more alert and will speak after the tube comes out.
"You notice I'm speaking in the present tense ... because that's where all your future prayers are going to come in," she wrote.
The e-mail said Giffords' parents are "humbled by the outpouring of love and prayers and overwhelmed with gratitude." The hospital's front lawn and the perimeter of Giffords' Tucson office are "illuminated by thousands of candles, get-well placards, hers and the other victims' photos, prayers, stuffed animals and people."
Surveillance video of the January 8 shooting shows Loughner walking up to Giffords and firing at her face from 24 to 36 inches away, Kastigar, told CNN.
Kastigar said he viewed the surveillance video the day of the incident, and the hard drives have been turned over to the FBI. He said its contents have not been previously discussed for a variety of reasons, chief among them protecting the victims' families from the graphic details it contains.
On the video, the suspect can be clearly seen walking around a table and up to Giffords, pointing a gun at her face and pulling the trigger. Giffords is barely in the frame of the video, he said. The gunman then turns to his left and walks out of the video, when witnesses said he began firing indiscriminately at others.
U.S. District Judge John Roll can be seen on the video putting his arms over Giffords staffer Ron Barber and attempting to push him down and crawl under the table with him, Kastigar said. In trying to help Barber, Roll exposes his back to the gunman and is shot. Roll died; Barber was also shot, but survived.
"I have to detach my personal feelings" about the video as an investigator, but the video offers investigators a way to sort out sometimes confusing or conflicting witness statements about what took place, Kastigar said. It also clarified that the gunman's intended target was Giffords, as it made clear that he walked up and fired the first round at her, Kastigar said.
A law enforcement official said federal and local authorities have conducted more than 300 interviews as part of the investigation.
CNN's Susan Candiotti and Roni Selig contributed to this report