US Crime Rates Falling - Why?

According to figures from the FBI, crime rates have steadily dropped since 1991. Several theories were put forth in a BBC article:
BBC: US Murder & Robbery Rates Drop

1. The Obama effect
2. Less demand for crack
3. Smarter policing
4. CompStat
5. Availability of legal abortion
6. More criminals behind bars
7. Decrease in children exposed to lead in petrol
8. Baby boomers grew up, less children born
9. Videogames keep would-be criminals occupied
10. Proliferation of camera phones

For much more details, check out the BBC article above.

I think it must be several factors at work. Perhaps even the fact that the world has become so much smaller since the conception of the Internet.

Regardless of the reason, it's heartening to know that the rates are dropping.

What do you think is causing the crime decrease.