This is a 2004 story, but you can still see a picture of the famous Escondido Library Cat (L.C.) there.
VISTA Jurors found Friday that a disabled man’s civil rights were not violated when his assistance dog was attacked by the Escondido library’s pet cat. The jury refused to award him damages.
More links to that cat (which died in 2003).
This is a true story. Often, ridiculous untrue law stories circulate (see earlier entry).
The Urban Legends Reference Pages at snopes.com defuse some such stories, and further down on the page are summaries of a few true legal stories that are just as ridiculous (including the story of the 12 lb. LC attacking the 50 lb. dog).