User blog comment:DancePowderer/After the Mayhem/@comment-3177613-20130809184154/@comment-1595565-20130809211348

We don't know what he did. For all we know, he either moved really fast or no one saw it. And besides, this is later, after Bellamy, rather than kill Luffy, exposed him and made it look like he made an effort to kill him. The other competitors know of it, but not Gatz or the audience.