Has there ever been a more obvious “whodunit” killer besides Dr. Quentin Costa?

Wife and I are watching Nip/Tuck for the first time, and how obvious was it that a new character is introduced at the same time as the serial killer character? Like, who else could it be?

He was obvious, but I have to admit that the sister being an accomplice was a surprise. The interrogation scene with them had me believing she wasn’t part of it.