The man accused of a mass shooting in Arizona pleaded not guilty Monday afternoon to federal charges against him, including the attempted assassination of Arizona Rep. Gabrielle Giffords and the attempted murder of two of her aides.

Jared Loughner, 22, is the only person facing charges in connection with the Jan. 8 shooting rampage outside a Tucson, Ariz. grocery store, which left six people dead and 13 others -- including Giffords -- wounded.

Giffords had been meeting with members of the public for a so-called "Congress on Your Corner" event when the shooting began.

Loughner appeared relaxed during his brief appearance, smiling as he entered the Phoenix courtroom clad in glasses and an orange prison jumpsuit. Eight U.S. Marshals were also minding the proceedings.

The case against Loughner involves many legal issues and experts say it could take years to complete.

Currently, Loughner faces charges at the federal level for the alleged shooting of federal government employees, including Giffords. But state authorities also intend to charge Loughner for the shooting and killing of civilians at the shopping centre.

Jurisdictional issues are also a concern for those prosecuting the case. To date, the case is being handled in Phoenix, but the U.S. attorney for Arizona has asked the court to move it back to Tucson to make it easier for victims and witnesses to attend future hearings.

The judge did not rule on that request during Monday's proceedings. Loughner's lawyer, Judy Clarke, has said she does not oppose moving her client to Tucson. The case was moved to Phoenix because one of the victims killed, U.S. District Judge John Roll, was a federal judge.

There are also questions about Loughner's state of mind, which CNN reporter Paul Vercammen said is a key concern of investigators at this time.

"Back in Tucson, you've got investigators looking into all sorts of things in Loughner's past, trying to find out where possibly things might have gone wrong for him and if he's mentally capable to stand trial," Vercammen told CTVs Canada AM from Phoenix on Monday morning.

Loughner's mental state may also be a factor in his defence strategy, with some experts predicting that he could mount an insanity defence.

Michael Piccarreta, a veteran Tucson lawyer who practised criminal defence for 30 years, said it appears that Loughner has a history of mental issues.

"It appears the actual guilt or innocent of the shooting will not be difficult to prove, and his pre-shooting behaviour seems to be a history of erratic behaviour -- issues of pre-existing mental illness," Piccarreta told The Associated Press in a recent interview.

At Monday's court appearance, U.S. District Judge Larry Burns of San Diego asked Clarke if there are concerns about her client's ability to understand the charges he faces.

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

Prosecutor Wallace Kleindienst said it would be another 30 days before he would decide whether Loughner will face additional federal charges. According to Kleindienst, prosecutors have given the defence records retrieved from Loughner's computer, as well as transcripts of about 250 interviews.

The judge scheduled a hearing to consider motions in the case for March 9.

Though it was initially reported that Giffords had died in the shooting, the 40-year-old congresswoman survived her injuries and has defied doctors' expectations in her recovery so far.

After spending two weeks at a medical facility in Tucson, she was moved to Houston's Memorial Hermann Texas Medical Center Hospital on the weekend, where she will receive therapy and eventually be transferred to a nearby centre for a lengthy rehabilitation program.

Despite her progress, doctors at Memorial Hermann had to insert a tube to drain a buildup of fluid in her brain, meaning Giffords will remain in intensive care.

But even with that setback, Mark Kelly, the injured congresswoman's husband, wrote on his Twitter feed that his wife began her rehab on the weekend.

Mark Kelly, the injured congresswoman's husband, wrote on his Twitter feed that his wife began her rehab on the weekend.

"Gabrielle starts her second day of rehab in 20 minutes at Memorial Hermann," Kelly said through Twitter on Sunday. "No weekends off here."

With files from The Associated Press