George Harrison photographs and lyrics have been stolen from the car of the late Beatle's sister, she has said.
George Harrison died of cancer in 2001
Lou Harrison said her car window was smashed and a briefcase containing pictures of her with her brother, and lyrics to his songs, was removed.
She was in the middle of donating memorabilia to the Clinton Presidential Library in Little Rock, Arkansas.
Lou Harrison asked fans to help find the items. "Maybe they could keep an eye on the internet," she said.
She told local TV station KTHV the items were "precious to me obviously because I don't have my brother in person any more".
The guitarist died in Los Angeles in 2001, after losing his fight against cancer.
His sister had taken the items from her home in Illinois to the library, which is being built by former President Bill Clinton and will be opened on 18 November.
She said she decided to donate the memorabilia because "Clinton is the Beatle president".
"There's not enough things to leave for my grandchildren," she said.
"So I thought maybe if I could house them at the Clinton Library, where they could be on display, that all the Beatle people could enjoy seeing them."