"Twitter founders ... knew Macgillivray at Google and hired him" (about PRISM)

Seems that they hired him from Google back in 2009:

http://bits.blogs.nytimes.com/2009/07/11/twitter-nabs-a-lega...

And it looks like Google joined PRISM back in 2009 according to the slides:

http://www.pocket-lint.com/news/121556-leaked-prism-slides-r...