This might be speculation, but during learning yesterday we discussed how would people have known if the cohenim brought the sacrifice with the blemish on its lips? Would Bar-Kamtza have found another way to cause trouble?
Also Zechariah's modesty lead to all this, so why did they listen?
Chabad translation: http://m.chabad.org/library/article_cdo/aid/404863/jewish/Kamtza-and-Bar-Kamtza.htm
http://www.chabad.org/media/pdf/323/YIxQ3233957.pdf
TALMUD, GITTIN 55–56