Of course he didn't. But he's clearly responsible for her death.
In the episode "Road Kill" Arthur Mitchell was about to kill himself by jumping from a roof and Dexter saved him!! All because HE wanted to be the one who kills Trinity! So if there are still people who think Dex works on justice, this is the clear example that his priority isn't serve justice or protect innocents, it is to fulfill his insane ritual like every serial killer.
I like Dexter, I feel sorry for him, but if the show had to have some realism, it would be imposible that Dex had a happy ending. He was already lucky enough to get away with Doakes's death, theBay Harbour Butcher incidentand also those innocent guys he killed in previous episodes (the child abuser who was stalking Astor, and the guy he killed by mistake in "Slack Tide"). Which by the way, he didn't feel remorse enough to stop killing.
He's responsible for Rita's death, that's it.
What do you think??