This mug shot released by the Pima County Sheriff's Office...

This mug shot released by the Pima County Sheriff's Office shows shooting suspect Jared Loughner. Loughner is accused of fatally shooting six people and critically wounding a congresswoman at a Tucson, Ariz. political event on Jan. 8, 2011. Credit: 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, and 13 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.

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

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

Investigators have said Loughner was mentally disturbed and acting increasingly erratic in the weeks leading up to the shooting. If he pleads not guilty by reason insanity and is successful, he could avoid the death penalty and be sent to a mental health facility instead of prison.

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.

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.

Giffords and two of her aides were among the 13 shooting victims who survived the attack. The six who died in the attack include U.S. District Judge John Roll and a 9-year-old girl.

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