Some people believe that some chimps CAN plot some things or make plans, before the time comes and suddenly attack. One chimp was seen collecting a bunch of rocks, waiting patiently for the zoo to open and seeing visitors come by, and the chimp all of a sudden threw rocks at them but lucky no one was hurt at the scene. 
and that's only because his aim was extremely poor. However it is possible that he can improve his aim someday.
Chimpanzee in Sweden plots and executes attack on zoo visitors | Outposts | Los Angeles Times
And another update to the story on Nash.
http://www.foxnews.com/story/0,2933,508264,00.html
