Donald Trump is no stranger to conspiracy theories. Mother Jones recently reported some of Trump's thoughts on asbestos. The toxic material "got a bad rap," Trump wrote in his 1997 book The Art of the Comeback, adding that he believed the mafia was behind the asbestos removal frenzy because "mob-related companies" often were awarded the removal contracts.

However, that's not the only time the well-known carcinogen caught Trump's attention. For years, one theory of the collapse of the World Trade Center towers has centered around a change made part way through construction of the buildings. According to the Port Authority, asbestos was used only up to the fortieth floor in one tower and not at all in the other. Due to concerns about asbestos in the 1970s, different fireproofing materials were used for the remainder of the project. While some have blamed the switch for the collapse, most have concluded that the intensity and high temperatures doomed the buildings regardless of the material used.

As recently as 2012, Donald Trump still subscribed to the asbestos theory. Commenting on Twitter, Trump wrote:

If we didn't remove incredibly powerful fire retardant asbestos & replace it with junk that doesn't work, the World Trade Center would never have burned down.

.@dubephnx If we didn't remove incredibly powerful fire retardant asbestos & replace it with junk that doesn't (cont) http://t.co/d10u18dh — Donald J. Trump (@realDonaldTrump) October 17, 2012



Trump did not respond to anyone who commented on his tweet and has not returned to the subject since—at least not on Twitter.