Reporters camped out at the suburban home haven't seen any sign of Jared Loughner's parents, but sources told CBS News that the FBI was able to speak with them.
Loughner's parents put a ply wood blockade in front of their gate to keep the media out. The FBI agents knocked, waited five minutes outside, and then went in.
The 22-year-old is accused of killing six people on Saturday - including a federal judge - and injuring 14 others, including U.S. Rep. Gabrielle Giffords. He is beingand has been assigned a lawyer who defended Oklahoma City bombing conspirator Timothy McVeigh.
Investigators said Sunday they carried out a search warrant at Loughner's home and seized 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. Saturday's shooting occurred at a similar event.
Other evidence seized from his home included an envelope from a safe with messages such as "," "My assassination" and the name "Giffords" next to what appears to be Loughner's signature. Police say he purchased the Glock pistol used in the attack in November.
Loughner lives with his parents about a five-minute drive from the shootings, in a middle-class neighborhood lined with desert landscaping and palm trees.
Neighbors said Loughner kept to himself and was often seen walking his dog, almost always wearing a hooded sweat shirt and listening to his iPod.
Loughner entered a Phoenix courtroom Monday handcuffed and wearing a tan inmate uniform. His head is shaved and he has a cut on his right temple.
His expression was impassive as he walked in, looked straight at the crowd at the back of the room packed with reporters, then turned around to speak to his attorney, Judy Clarke. He responded "yes" when asked if he understood his rights.
The courtroom was under heavy guard with about a dozen U.S. marshals.