Who did it and why?

No, sci fi doesn't explain it. Building 7 was hit by debris. Again, from those puppets over to Popular Mechanics, about halfway down the page:

http://www.popularmechanics.com/technology/military/news/debunking-911-myths-world-trade-center#wtc7

When things collapse, it's usually pretty "sudden". Or at last seems that way. In truth, a collapse is the culmination of supports failing over a period of time. Either a short period of time, like a controlled demo, or over a period of time, like the Towers and building 7. Or the facade at the Pentagon.

Sorry, but Occam's Razor strikes again.

Hendrix had nothing to do with the Panthers. As rock stars of the day went, he was pretty apolitical. He was about dope and banging white girls. He also enjoyed only about a year or so of popularity in the States before his death. He was huge in England before he came here, and was of the mind to reside in England. As for how to "deal with" celeb malcontents, Hoover was more for discrediting them than killing them. He was afraid of creating martyrs.

No, Hendrix was a novice junkie who got a hotshot.