According to this article I found on google (had to use the google cache, couldn't find it on the search on the site - ready your tinfoil hats everyone!) http://www.freerepublic.com/focus/f-news/1529700/posts?q=1&&page=151
It was flight 621 from LAX to Chicago.
Gahh, wrong link!
http://66.102.7.104/search?q=cache:bPITQnT1SmMJ:www.kyw1060.com/news_story_detail.cfm%3Fnewsitemid%3D50753+lax+missile&hl=en&lr=lang_en&client=firefox-a