Let's set the scene: five Cal Berkley students crashed Stanford's preseason basketball party "Cardinal Chaos". Afterward, they see the tree costume being loaded into a car, and a devious plot forms in their minds.
They follow the tree to Stanford's Band Shak, where another, much more inebriated party was going on. After the party concluded, the quintet snuck in and poached the pine, taking it back to Berkley.
Needless to say, Cardinal students were less than thrilled, and the Stanford PD immediately began looking for leads on Berkley's campus. Several ransom notes were delivered to Stanford in the form of letters written to Cal's newspaper, The Daily Californian, written by the students under the pseudonym "The Phoenix Five". There was plenty of trash talk going on in them, and Cal's dean of students ordered the tree be returned.
Eventually, the tree was, in fact, given back, only to be burned by Stanford students who saw it as "Contaminated". A new tree was revealed during The Big Game of that year.
This was the best of all the thefts chronicled in this article, because of the rivalry and the fact that the costume was burned upon it's return.