Jared Lee Loughner pleaded not guilty on Monday to three charges of attempted murder for allegedly trying to kill Rep. Gabrielle Giffords (D-Ariz.) and two of her aides.

The Associated Press reported that Loughner, 22, entered the plea in a Phoenix federal court just after 1:30 p.m. Mountain Time. The suspect's court appearance was his second since Jan. 8, when he allegedly opened fire on a crowd at a public event for Giffords in Tucson. Six people were killed and 13 were injured, including Giffords, who was shot in the head.

If Loughner is found guilty of attempted murder of a member of Congress, he could be sentenced to life in prison; if he is convicted of attempting to kill a federal employee, he could face a maximum of 20 years in prison.

Giffords on Friday was moved from the University Medical Center in Tucson to TIRR Memorial Hermann Rehabilitation Hospital in Houston, where she will receive further treatment.

Loughner was ordered held without bail on Jan. 10, two days after the shooting. He was indicted last week on the three attempted murder charges, which prosecutors described as an "initial" indictment.

Federal prosecutors are expected to file murder charges against Loughner for allegedly killing federal district court Judge John Roll and Giffords staffer Gabriel Zimmerman. Additionally, Arizona is expected to charge Loughner for the other shootings.

Federal prosecutor Wallace Kleindienst said that he would know within 30 days whether the federal government will file additional charges against the suspect. According to the Arizona Republic, he added that his team provided Loughner's defense attorneys with files from Loughner's computer and 250 interviews conducted during the investigation. 

The Republic also reported that Loughner's well-known defense attorney Judy Clarke decided not to address questions surrounding her client's mental capability to stand trial at this point. She also did not object to a prosecutor's motion to move the hearings back to Tucson, where many of the survivors, victims and their families reside.

About 110 people attended the hearing, according to the Republic, and eight U.S. Marshals guarded the courtoom.

U.S. District Judge Larry Burns set Loughner's next court date for March 9 at 1:30 p.m. The date for the suspect's trial will likely be set at that hearing.

-- This post was updated at 4:27 p.m.