TUSCON, Ariz. — Federal prosecutors brought charges today against the gunman accused of carrying out an assassination attempt on Rep. Gabrielle Giffords and killing six people at a political event in Arizona.

Investigators said they carried out a search warrant at Jared Loughner’s home and seized an envelope from a safe with messages such as “I planned ahead,” ”My assassination” and the name “Giffords” next to what appears to be the man’s signature. He allegedly purchased the Glock pistol used in the attack in November at Sportsman’s Warehouse in Tucson.

Court documents also show that Loughner had contact with Giffords in the past. Other evidence included a letter addressed to him from Giffords’ congressional stationery in which she thanked him for attending a “Congress on your Corner” event at a mall in Tucson in 2007.

Heather Williams, the first assistant federal public defender in Arizona, says the 22-year-old suspect doesn’t yet have a lawyer, but that her office is working to get a lawyer appointed for Loughner.

Meanwhile, authorities released 911 calls in which a person witnessing the mass shooting outside a grocery store in Tucson describes a frantic scene and says, “I do believe Gabby Giffords was hit.”

Loughner, 22, is accused of killing six people, including a federal judge, an aide to Giffords and a 9-year-old girl who was born on Sept. 11, 2001. Fourteen others were wounded, including the three-term Democrat lawmaker. Authorities don’t know his motive, but said he targeted Giffords at a public gathering around 10 a.m. Saturday outside a busy Tucson supermarket.