Forty-six flag standards were found empty and another 33 flags were in charred tatters Sunday in the cemetery, authorities said. Swastikas drawn on paper appeared where 14 of the flags had been.
Members of the American Legion on this island off Washington's northwest coast replaced the burned flags with new ones Sunday afternoon.
The vandals struck again on Memorial Day after a guard left at dawn, the San Juan County sheriff's office said. This time, the vandals left 33 of the hand-drawn swastikas.
"This is not an act of free speech. This is a crime," Sheriff Bill Cumming said in a statement released Monday afternoon.
Investigators believe there's more than one culprit, based on the number of flags that were vandalized, Cumming said in a telephone interview. But authorities have no suspects, he said.
The sheriff said deputies were trying to lift fingerprints off what little physical evidence they were able to recover.