My link
Here are all the "innocent" kills on Dexter:
Oscar Prado, Miguel Prado's brother - Self defense, the first accidental break of Harry's code, he thought he was a junkie coming for drugs trying to kill him, but he was in fact a drug user on the mend, protecting his house. He worked with at risk kids and had a few parking tickets.
Camilla Figg - Euthanasia, the first intentional break of Harry's code, at Camilla's request. She was on her death bed, not wanting to suffer anymore, and so he brought her her favorite Key Lime Pie, laced with poison.
John Farrow - Incorrect evidence, Dexter thinks this photographer who has been accused of violent acts before and stages elaborate death scenes in his art is clearly a killer. However, it later turns out, with air tight evidence, that his assistant was the killer all these years.
Rankin - Rage, Dexter's first killing of a potential innocent bystander. A guy in a bathroom talks smack to Dexter immediately following his wife's death. He loses it and beats him to death. His inner voice dad says "That's the first human thing I've seen you do."
Stan Liddy - Self Defense, a corrupt ex-cop determined to get back on the force by busting Dexter, he traps Dexter in "a van down by the river." A knife fight ensues, and Dexter has no choice but to defend himself.
Looks like Farrow is the one