PHOENIX -- The FBI and the Pima County Sheriff's Office have finished their investigations into the mass shooting in Tucson that killed six people and wounded 13, including Congresswoman Gabrielle Giffords.

Spokesmen for both agencies told The Associated Press on Wednesday that the investigations are complete.

Sheriff's spokesman Jason Ogan said his agency's case was turned over to the FBI. FBI spokesman Manuel Johnson said all materials were turned over to the U.S. Attorney's Office for prosecution.

Investigators interviewed dozens of people who knew 22-year-old Jared Loughner, who is accused of carrying out the Jan. 8 shooting outside a Tucson grocery store that killed a 9-year-old girl and a federal judge, among others.

They also searched Loughner's home and car and seized various items, including his computer.