TUCSON - The suspect in the Arizona shooting rampage that critically injured a U.S. congresswoman pleaded not guilty Wednesday to federal charges accusing him of killing six people and wounding 13 others.

U.S. District Judge Larry Burns also approved the release of some records of a police search of Jared Lee Loughner's home.

Loughner, who smiled as he was led into the courtroom, appeared before Burns in kaki prison clothes, his once-shaved head now featuring short, dark hair and side burns. He pleaded not guilty to charges that included trying to assassinate U.S. Rep. Gabrielle Giffords, attempting to kill two of her aides and murdering federal judge John Roll and Giffords staffer Gabe Zimmerman.

Loughner also is charged with causing the deaths of four others who weren't federal employees, causing injury and death to participants at a "federally provided activity" and using a gun in a crime of violence.

He also will likely face state charges stemming from the Jan. 8 attack at a Giffords event outside a Tucson grocery store.

News organizations had asked Burns to unseal records related to the search of Loughner's home.

The Arizona Republic newspaper and KPNX-TV argued there was no basis for search warrant records to remain sealed and that the public has a right to the records. The documents have been sealed since Jan. 11.

Loughner's attorneys argued their client's right to a fair trial might be harmed by the release of the records. The said the documents contain potentially inflammatory statements by a law enforcement officer.

Burns ruled Wednesday that many of the records should be released. However, he said some will remain sealed, such as information that is inflammatory or that will not be admissible at trial.

Loughner's father attended the hearing, listening to the proceedings with his arms crossed, head down and eyes closed.

Also in the crowded courtroom were more than 20 U.S. Marshals and security personnel, numerous reporters, about a dozen family members of victims, and at least two survivors of the shooting spree, Susan Hileman and U.S. Army Col. (Ret.) Bill Badger.

Hileman, 58, was shot three times in the attack. She was holding 9-year-old Christina Taylor Green's hand when the shooting erupted, and Christina was killed.

Badger, 74, was grazed by a bullet in the back of the head. He is credited with helping to subdue Loughner at the scene.