Sheriff's spokesman Jason Ogan said his agency's case was turned over to the FBI, although he did not know when. FBI spokesman Manuel Johnson said all materials have been turned over to the U.S. Attorney's Office for prosecution.
Investigators interviewed witnesses and survivors of the Jan. 9 shooting outside a Tucson grocery store that killed a 9-year-old girl and a federal judge, among others. They've also interviewed parents, friends and others who know 22-year-old Jared Loughner, who is accused of carrying out the shooting.
Investigators combed through Loughner's home, where he lived with his parents, and seized his property, including a computer and handwritten notes found in a safe that read "I planned ahead," ''My assassination" and "Giffords." One note said "Die, bitch," which authorities believe was a reference to Giffords.
Prosecutors say an expert will need a sample of Loughner's handwriting to determine if he wrote the documents.
Loughner will be tried first in federal court before any prosecution begins on state charges.
Loughner pleaded not guilty to federal charges of trying to assassinate Giffords and kill two of her aides. The indictment specifying those charges superseded an earlier federal complaint that also charged him with murder for the deaths of U.S. District Judge John Roll and Giffords aide Gabe Zimmerman.
Another indictment is expected to restore those murder charges.
Loughner's next court hearing is set for March 9.