Did the creators of HDTF use assets from other mods without permission?

This appears to be the reason for a lot of complaints in the forums, but according to the developers, including game director Berkan Denizyaran, who I spoke to on the phone, and a member of Royal Rudius Entertainment, who answered a few questions via email: no, there are no stolen assets in the game. An early demo of the HDTF did use assets from other mods, I was told, but they were used as placeholders during development. The developers say these placeholder assets are not present in the finished product.

The Steam forums are filled with posts from users comparing various textures and assets to those from other games and mods, and it can be a bit of a nebulous process trying to verify their accuracy, what version of the game they're from, and if these assets are in fact taken from other mods or games. However, a member of the team of one of the mods in question, Holymac from Firearms: Source, posted in the Steam forums that the team had looked into it and didn't see any of their work being used.

"Our art team determined that upon a cursory look of the content released with the demo," wrote Holymac, "and assets the HDTF team provided willingly, it appears no theft of intellectual property has taken place."

I sent a follow-up email to the Firearms: Source team to ask if they had done any more investigation since January, and received a response from project coordinator Vincent Micelo, stating: "The source content in question was inspected by some of our team members and they agree that it is original content. We have no further statements."

The developers of Hunt Down The Freeman also point out that just because an asset looks familiar, doesn't mean it's been stolen. In an email to PC Gamer, Gabe, who identifies himself as Head of PR for Royal Rudius Entertainment, writes:

"People have found assets that they stated were stolen, but then we've given them the source we bought it from, like the US soldiers in our game, they are from TurboSquid, a site where you can buy models and use them for commercial purposes. Another example would be a shot-up car from S.T.A.L.K.E.R. was found in our game and paraded as definitive proof that we were stealing. It took me three minutes to find the car, and it was in one of L4D2's DLC files, of which we have permission to use."