TUCSON, Ariz. (AP) -- The man accused of carrying out a mass shooting in Tucson pleaded not guilty Monday to charges he tried to kill Rep. Gabrielle Giffords and two of her aides.

The plea by Jared Lee Loughner marked his second court appearance since he allegedly shot the congresswoman and 18 others at Giffords' meet-and-greet event on Jan. 8 outside a grocery store in Tucson. Six people died, including U.S. District Judge John Roll and a 9-year-old girl. Thirteen others were wounded.

Loughner, 22, faces federal charges of trying to assassinate Giffords and attempting to murder two of her aides. He will later face state charges dealing with other victims.

At least eight U.S. Marshals were present at the hearing in the Phoenix courthouse, where Loughner entered Monday afternoon smiling and wearing an orange prison suit and glasses. His hair, shaved in the mug shot that's become an enduring image of the tragedy, has grown out slightly.

Investigators have said Loughner was mentally disturbed and acting increasingly erratic in the weeks leading up to the shooting. If his attorney uses mental competency questions as a defense and is successful, Loughner could be sent to a mental health facility instead of being sentenced to prison or death.

U.S. District Judge Larry Burns of San Diego asked Loughner attorney Judy Clarke whether there was any question about her client's ability to understand the case against him.

"We are not raising any issues at this time," Clarke said.

Giffords was shot in the forehead and spent two weeks in a Tucson hospital before she was flown to Memorial Hermann Texas Medical Center Hospital on Friday. Shortly after her arrival, doctors said she had been given a tube to drain a buildup of brain fluid that has kept the Arizona congresswoman in intensive care.

The Houston hospital treating Giffords gave no update Monday, and spokesman James Campbell said the next update would come when they are ready to move Giffords to the rehab hospital.

A hospital statement said Giffords would continue to receive therapy "until her physicians determine she is ready for transfer" to a nearby center where she would begin a full rehabilitation program.

Prosecutor Wallace Kleindienst estimated that he would know within the next 30 days whether additional federal charges would be filed against Loughner. Kleindienst said prosecutors provided defense lawyers with records taken from Loughner's computer and documents of about 250 interviews made in the case.

The judge did not rule on prosecutors' request to move the federal case back to Tucson so that victims and witnesses do not have to make the four-hour round trip drive to Phoenix to attend court hearings. The case was moved because one of those killed, Roll, was a federal judge.

Clarke said she didn't oppose the request, but questioned where Loughner would be jailed in Tucson if the case were moved.

Clarke has not responded to requests seeking comment. She is one of the top lawyers in the country for defendants facing prominent death penalty cases, having represented clients such "Unabomber" Ted Kaczynski and Olympic bomber Eric Rudolph. She has a reputation for working out plea deals that spare defendants the death penalty, as was the case for Rudolph and Kaczynski.

The judge set a March 9 hearing to consider motions in Loughner's case.