Do they really think that a second investigation is going to suddenly uncover new evidence that supports the controlled demolition theory?

And what if, after this new investigation, they conclude that the building collapsed due to fire as originally presented in the NIST report? Will AE911Truth suddenly pack it up and shut down?

You could have an investigation conducted by a private, vetted team of experts, where every minute detail and every piece of evidence is collected according to strict scientific chain of custody rules, and every step of the investigation is under a microscope of scrutiny on both sides of the issue. But if the final summary concludes that it was fire that caused the structural failure and subsequent collapse of WTC7, the truthers will just keep bitching and moaning that something somewhere was corrupt and proclaim that the whole investigation was a sham.

Nothing will convince the devout zealots that they're side is right and the rest of the world is wrong. The truthers will never believe anything that doesn't support their position. Ever.