First, Zach puts on a very convincing show of innocence when Dex and Hannah encounter him in the Keys. Not only that, but Zack - without knowing that Dex found Zach's blood under Hannah's fingernail - gives Dexter an explanation for the blood: Zach cut his finger on his car door, and his blood was "everywhere". Presumably this could have included something that Cassie touched when Zach was leaving Dex's apartment building.
But if Zach did not kill Cassie, who did?
I've been suspicious all season of Dr. Vogel. But what would her motive have been for killing Cassie?Nonetheless, I was so suspicious of Vogel I half expected her to poison Hannah or Zach or both over dinner.
But Zach is to soon die another way - courtesy of the brain surgeon, apparently, who sends along the specimen from Zach's brain to Dr. Vogel (unless she brought the specimen back home herself).
So, who killed whom here? I see three possibilities:
1. Zach did kill Cassie, and Vogel killed Zach because she didn't want this failed experiment in the code walking around.
2. Vogel killed Cassie and Zach - but what (again) was Vogel's motive for killing Cassie? She thought her nosiness was a threat to Dexter? A little weak.
3. Someone we don't yet know killed both. But if that's another brain surgeon, Cassie's brain was still intact, which doesn't fit the MO.
I guess I'd choose #1 - which would make Dr. Vogel a super-psycho.
One thing we can be sure about is neither Dexter nor Hannah did any killing this time - they were too busy making good love when Zach was killed, for sure. I'm glad they're together now - it's a great moment in the series. But if Vogel is the killer, then Hannah will soon be a target. Actually, that will be the case whoever the killer is, for the killer is clearly keyed into Dex's life.
One thing we can also be sure of is the killer didn't spend any time in the Hatch - because that was from Lost, though Mama Cass's "Make Your Own Kind of Music," first heard in a television series to such good effect on Lost, is now playing at crucial junctures in Dexter.
See also Dexter Season 8 Premiere: Mercury in Retrograde, Dexter Incandescent ... Dexter 8.2: The Gift ... Dexter 8.3: The Question and the Confession ... Dexter 8.4: The "Lab Rat" and Harry's Daughter ... Dexter 8.5: Just Like Family ... Dexter 8.6: The Protege ... Dexter 8.7: Two Different Codes?
And see also Dexter Season 6 Sneak Preview Review ... Dexter 6.4: Two Numbers and Two Killers Equals? ... Dexter 6.5 and 6.6: Decisive Sam ... Dexter 6.7: The State of Nebraska ... Dexter 6.8: Is Gellar Really Real? .... Dexter 6.9: And Gellar Is ... ... Dexter's Take on Videogames in 6.10 ...Dexter and Debra: Dexter 6.11 ... Dexter Season 6 Finale: Through the Eyes of a Different Love
And see also Dexter Season 4: Sneak Preview Review ... The Family Man on Dexter 4.5 ...Dexter on the Couch in 4.6 ... Dexter 4.7: 'He Can't Kill Bambi' ... Dexter 4.8: Great Mistakes ...4.9: Trinity's Surprising Daughter ... 4.10: More than Trinity ... 4.11: The "Soulless, Anti-Family Schmuck" ... 4.12: Revenges and Recapitulations
And see also reviews of Season 3: Season's Happy Endings? ... Double Surprise ... Psychotic Law vs. Sociopath Science ... The Bright, Elusive Butterfly of Dexter ... The True Nature of Miguel ...Si Se Puede on Dexter ... and Dexter 3: Sneak Preview Review
See also about Season 1: First Place to Dexter