Peter Michael Ketcham, an iPhone app developer from Wisconsin, has a masters degree in mathematics and worked as a mathematical data visualization programmer at NIST from 1997 to 2011. He had no involvement in the 9/11 investigation (or any other investigation), and has no background in structural engineering or physics. And yet the 9/11 conspiracy theory group Architects and Engineers for 9/11 Truth (AE911) is strongly promoting a letter he wrote that was published in Europhysics News, (which last month published an article by AE911). The letter is: http://www.ae911truth.org/images//PDFs/Peter_Ketcham_EPN_LTE.pdf So what we have here is just some guy who watched the 9/11 documentaries, and became convinced by them. Nothing wrong with that per se, the documentaries can be quite convincing - most documentaries are, that's their function. But he's just some guy, like me (I've even done work on computational fluid dynamics, and developed iPhone apps). The fact that he worked on mathematical visualizations at NIST is entirely irrelevant. It's an example of an appeal to false authority. AE911 are claiming that there's something significant here because, as their email headline puts it "BREAKING NEWS: Former NIST Employee Speaks Out". AE911 describe his letter as "startling and extraordinary", a "stunning 500-word rebuke" and an "incredible development", when in fact if you look at the content of the letter it is simply a regurgitation of the talking points that AE911 have been using for years, like: "Free-fall acceleration" is something that AE911 say is evidence of controlled demolition, but it's also something that is in the NIST report, and is explained by the mode of collapse (the interior collapses first, then the exterior columns have no lateral support, so they buckled, leading to near zero resistance for at least part of the collapse). "An elaborate sequence of unlikely events" is in reference to NIST's description of a likely initiating incident, where thermal expansion of floor beams pushed a girder off its seat, starting the collapse. AE911 like to portray this as NIST saying this is the only possible thing that could have caused the collapse, so they nit pick the simulation, saying the seat was an inch wider, and it had stiffener plates welded to it making the failure condition distance greater, or they argue about the exact amount of thermal expansion, and they point to other differences between the NIST model and building plans, like the absence of sheer studs on the beams. AE911 (and presumably Mr Ketcham) say that because they have found these problems, then the entire NIST report is wrong. But by focussing on this one initiating incident (which may or may not have taken place) then move focus away from the bigger picture which was that NIST had identified multiple structural failures from the fires, any combination of which could have led to eventual collapse. In fact in the full scale simulations that NIST performed, the girder in question is not part of the initiating incident, so AE911's hyper-focussed objections are moot. Mr. Ketcham, like most people in the 9/11 "Truth" movement, means well. But he's really just some guy who has been convinced by AE911's arguments. Like me, he has no training or experience in structural engineering or physics, so there's no reason to accept his argument based on his experience any more than you would accept mine.