We'll never know who Jackie was referring to when she said "they".
However, in the context of today's liberal thought processes, "they" means the Vast Right Wing Conspiracy.
Leni
Funny you should mention that. MSNBC had a special on JFK the other nite. Chris Matthews was interviewing Hilary. She said something to the effect of "blah blah blah, I'll never forget when..." and then quoting Jackie, " I want them to see what THEY did to my husband." I believe Hilary repeated that quote, and with emphasis. She was getting her right wing conspiracy point made.