User blog comment:MilitaryBrat/Lord Voldemort vs Darth Vader/@comment-4552610-20111219220745/@comment-2006360-20111220022137

There you go again! WRONG! The Killing Curse isn't slow at all.

Although it isn't confirmed to have been spoken nonverbally in the books, Avada Kedavra has been casts as such in the movies, notable the last one (or so speculated).