There are rumors spreading since last weekend's episode that Jordan Chase may have murdered Rita, and not Trinity. Take it as you will, however, I do find it to be a very interesting theory (even if a little far fetched, but hey, I would've never seen any of the other twists in this show coming, so you never know)
Anyways, here are some of the leading "clues" that support these theories.
1. Rita's death didn't match Trinity's other kills. For one, it broke his cycle. Trinity also usually used towels to make sure no blood seeped out into the bathroom. The way in which Harisson was found is very similar to how Dexter was found as a child, possibly meaning that whomever did kill Rita knew quite a bit about Dexter's past (it may just be a coincidence, but you never know)
2. Jordan Chase shows not only an odd interest in Dexter, but also in Trinity (as he confessed). He followed the Trinity case closely, and it's possible that he admired him for his work (enough to carry out a murder in a similar fashion, as part of his "take it now" philosophy). Also, there was an exchange of looks between Chase and his head of security as Dexter exited the room after their meeting. Dexter doesn't come off as suspicious or dangerous, so why the exchange of looks?
3. It may be possible that Chase has some relationship to Trinity. Some say that Trinity may be one of the men in the picture. Others say that he may have taught Chase and his serial killer friends how to kill. It may even be possible that Chase is a blood relative to Trinity.
4. The vial of blood shown in last weekend's preview for the new episode may be filled with Rita's blood, sort of a trophy like Dexter's blood slides.
5. Chase knew the name of Dexter's son. Suspicious, but it could be possible that it was mentioned in the news after Rita's death (which Chase followed closely)