Charles Austin Miller

Chosen answer: This can be a little confusing, but here goes: Early in the film, Boris escapes from the lunar prison and returns to Earth, confronting both agents K and J and telling Agent K that he's "already dead" (Boris was implying that he was going back to 1969 to kill K at the Apollo launch site, thus preventing K from deploying the ArcNet). When Boris does kill K in 1969, it changes the timeline, so only Agent J can remember K's existence in 2012. When Agent J goes to MIB headquarters the next day, he is baffled that nobody remembers K, and Agent J has to convince Chief Agent O that K was alive just the day prior. It is Chief Agent O who deduces the timeline fracture, and J suddenly understands that Boris killed Agent K in 1969 at the Apollo launch, preventing K from deploying the ArcNet (which necessitates J going back in time to save Agent K). Although J tried to keep all of this a secret from 1969 Agent K, he eventually admits to K that Boris killed K at the Apollo launch.

Charles Austin Miller