Since May 2009, officials have been on the lookout for a person who has been smearing mustard, mayo and other barbecue staples on more than 100 library books.
Boise police now say they've cracked the curious case of the condiments, arresting 74-year-old Joy L. Cassidy outside Boise's Ada County Library on Sunday. They said Cassidy had dumped an open jar of mayo into the library's book drop moments earlier.
"It's just senseless," Boise Police spokeswoman Lynn Hightower told AOL News. "The victims really are all the citizens who use the library. Those are taxpayer-supplied books, and destroying them is really senseless."
Hightower said Cassidy had caused thousands of dollars worth of damage. Cassidy was charged with misdemeanor injury to property and misdemeanor carrying a concealed weapon, after police said they found a loaded handgun under the front seat of her car. The Idaho Statesmen reported that she did not have a concealed weapons permit.
Investigators consider Cassidy a person of interest in about 10 other stealth ketchup, corn syrup and mayo attacks that have left library books soiled and sticky over the past year, but Cassidy has not been charged in those incidents.
Hightower said officers nabbed Cassidy in a classic stakeout of the library.
"They had been tracking the crimes, and they knew there was a pattern of what time of day the vandalism usually occurred," she said. "The officers were giving the library extra patrol and stopped a vehicle at the library drop box."
But one question remains unanswered: What prompted the alleged bandit to tarnish the city's books -- and waste jars and jars of perfectly good condiments?
"She did give officers some indication of a motive," Hightower told AOL News. "But that's not something we can release at this time."