Police are investigating the theft of roughly $75,000 worth of Grateful Dead memorabilia that was awaiting transfer to its new owners following last month’s Grateful Dead Family Jubilee Auction. The Northwest Herald reports that the items were stolen from Donley’s Auction Services in Union, IL at some point on April 25 or 26.

According to the Northwest Herald, the items were being processed—and some of them were awaiting pickup by an armored car—when they were taken. Evidently, the most valuable item stolen was an original, hand-painted 1966 Stanley Mouse/Alton Kelley Family Dog skull and roses poster. The reserve price for the piece was listed at $25,000 for the auction.

Three other posters were reportedly stolen as well, including a 1986 original Russelheim, Germany poster, a 1986 original Statue of Liberty tour poster and a 1966 “The Quick and the Dead” serigraph signed by artist Wes Wilson. The latter poster was the 12th image in the Family Dog series and marked the Grateful Dead’s first use of skeleton iconography.

The McHenry County Sheriff’s Department is asking for the public’s help in solving the case. Those with info can call the Sherriff’s investigation division at 815-334-4750 or give an anonymous top via Crimestoppers at 1-800-762-7867.