By Jacques Billeaud

PHOENIX — The suspect in the shooting of Rep. Gabrielle Giffords smiled and nodded but didn’t speak as he appeared in court Monday and his lawyer provided the 22-year-old’s first response to the charges: a plea of not guilty.

In the two weeks since the deadly attack that killed six outside a Tucson grocery store, Jared Loughner’s hair — shaved in the mug shot that’s become an enduring image of the tragedy — has grown out slightly.

The Tucson resident wore an orange prison jumpsuit and glasses, and his wrists were cuffed to a chain around his waist as eight U.S. marshals kept watch in the packed Phoenix courtroom and gallery above.

Loughner faces federal charges of trying to assassinate Giffords and kill two of her aides. More charges are expected.

Investigators have said Loughner was mentally disturbed and acting increasingly erratic in the weeks leading up to the attack on Jan. 8 that wounded 13.

If Loughner’s 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.

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 her in intensive care.

Loughner will likely face state charges in the attack, and also federal murder charges listed in an earlier criminal complaint for the deaths of Giffords aide Gabe Zimmerman and U.S. District Judge John Roll.

Those are potential death penalty charges, which require a more painstaking process under Justice Department rules.