Loughner, 22, has been charged on five counts – two of murder and three of attempted murder, according to the charge sheet filed by Arizona US Attorney Dennis K Burke. The alleged suspect is scheduled to be produced before a Arizona court later today.
Federal investigative authorities say Loughner tried to kill the Democratic Congresswoman, Gabrielle Giffords, who is battling for her life at a hospital in Tucson, Arizona.
Doctors say Giffords, who was shot at the back of her head, by Loughner at a public event at a grocery store in Tucson on Saturday is in a very critical condition though she is responding to the treatment.
The shootout also killed six others, including a nine-year-old girl and a federal district judge, besides injuring 18 others. Doctors said Giffords was lucky to be alive but would not speculate about the degree of her recovery, which they said could take months or longer.
"Overall this is about as good as it is going to get," said Dr Peter Rhee, the chief of trauma surgery at University Medical Center, where she was being treated.
"When you get shot in the head and a bullet goes through your brain, the chances of you living are very small and the chances of you waking up and actually following commands is even much smaller than that," he said.
US President Barack Obama, who on Saturday had dispatched the FBI Director Robert Mueller to Arizona to help coordinate the investigation, asked Americans to observe a moment a silence today to honor the innocent victims of the "senseless tragedy" in Tucson, Arizona.
He also signed a proclamation calling for flags to be flown at half-mast. Loughner was arrested by the police after the incident. Eyewitness described him as a young white man who looked like a "fringe character", clean-shaven with short hair and wearing dark clothing.
Pentagon denied news reports that he ever served in Army. He attempted to enlist in the Army but was rejected for service, the US Army said in a statement. The reasons for his rejection were not divulged.
Loughner shot Giffords with a semi-automatic open at point blank in her head. Immediately, he attempted to flee but was overpowered by her staff and others present at the function.
In an affidavit filed before the court, federal authorities alleged the suspect planned the attack in advance.
A search warrant was executed at Loughner's home wherein the authorities found a letter inside a safe that Giffords wrote to Loughner on August 30, 2007, thanking him for attending a "Congress on Your Corner" event, according to an FBI agent affidavit filed with a five-count criminal complaint.
"Also recovered in the safe was an envelope with handwriting on the envelope stating "I planned ahead" and "My assassination" and the name "Giffords," along with what appears to be Loughner's signature," the criminal complaint reads.
This comes as authorities announced that the man previously thought to be associated with the suspect has been cleared of any involvement in Gabrielle Giffords shooting. At a press conference, Mueller said Loughner may face additional charges under the domestic terrorism statute.
"This was an attack not only against dedicated public servants, but against our fellow citizens," he said. "This is an attack on out institutions and our way of life," Mueller said.
"As you know, Jared Lee Loughner was subdued by brave quick thinking individuals at the scene. He was taken into custody by sheriff deputies and is now in federal custody and formal charges are expected this afternoon," Mueller said.
Federal agents and deputy sheriffs are working around the clock to learn as much as possible, gather the facts, and determine why someone would commit such a heinous act and whether anyone else was involved, Mueller said.