I am confused...

Quick question about Lotb. Recently I have been replaying this story now that it is completed. I am now at the part where Scarlett and Cole took refuge in the catacombs and are chased by a Beast. But was it ever addressed anywhere exactly what beast were after them? Was it Adam? Another Beast made by the nazis? An experiment gone wrong? Nothing? Is there any kind of additional info about this because I honestly don't remember anybody ever mentioning it again. Thank you!