Board Thread:False Info and Speculative Discussion/@comment-27547895-20160208013829/@comment-26879545-20160208132009

^ When Chimeras die in their shifted state, they don't return to their human form like real shifters do. That's why he takes the bodies. If anyone were to see those bodies, it'd reveal that the supernatural exists and, according to the lore on hellhounds revealed to us thus far, it'd be against Parrish's job description to let them be found.

The reason Chimeras are not supernatural is because they were created through scientific methods versus magical Bites or from being born from a supernatural parent. IIRC, even Theo admitted they're not like real supernatural creatures; they're just cheap knock-offs manufactured in some sewer lab.