Here is a link to a good vid clip and story about it.
http://www.everydaynodaysoff.com/2010/02/28/airsoft-gun-seizure-apparently-toys-can-be-real-guns/
Just a few of issues a gunsmith found after analyzing both.
◦The WE TTI M4’s lack any sort of functional gas tube which is integral to an AR15’s operation
◦The upper receiver of an AR15 fits onto the lower of the WE TTI M4
◦The stock trigger pack in the WE TTI cannot strike the firing pin of a AR15 bolt
◦The body of the WE TTI lower is several mils thinner than an AR15 lower, and shims would be needed for any AR trigger pack to work
◦The trigger pack of an AR15 appears to be able to fit onto the lower receiver of a WE TTI M4, one of the AR15 trigger pack retaining pins is impossible to insert without major modification, and the hammer isn’t operable with the WE TTI lower.