I am a Harper's Island junkie. I read the message boards, watch the episodes online Thursday nights when Canada gets the show (US airs it on Saturday), and follow all the actors and producers on Twitter. I just love the show. Eleven episodes have aired and only two are left. US gets the final episodes July 11 while they air in Canada on July 9.
Like most "Harpies," I've been guessing who the killer is since episode one. I've always wondered whether it was the Sheriff (Jim Beaver) or Jimmy (CJ Thomason) or Beth (Amber Borycki) or Nikki (Ali Liebert). Now that all of these people are dead, with the exception of Jimmy, I have my final guess: the groom, Henry (Christopher Gorham). A poll at CBS.com says 40% (at the time I'm writing this) of the people agree with me. I did most of my brainstorming with people on the CBS, IMDb, and Harper's Globe boards. Everyone there has their own opinion, but the people on the Henry bandwagon make most sense to me.
There aren't that many choices. After episode 11, we are left with Henry (Christopher Gorham), Abby, Henry's best friend (Elaine Cassidy), Trish, the bride (Katie Cassidy), Sully, the cocky jerk best man that I somehow love (Matt Barr), Shea, Trish's sister (Gina Holden), Danny, a groomsman (Brandon Jay McLaren), Madison, the flower girl and creepy 9-year-old (Cassandra Sawtell), and Jimmy, Abby's love interest and a fisherman (CJ Thomason).
There's also a second killer who was revealed after episode 10 — John Wakefield (played by Callum Keith Rennie). According to producer Karim Zreik, he isn't the main killer. The main killer is someone I mentioned in the preceding paragraph. John Wakefield killed a lot of people in episode 11 — Nikki (Ali Liebert), Shane (Ben Cotton), Cal (Adam Campbell), and Chloe (Cameron Richardson). He also killed Abby's mother seven years ago. Abby's mother and he had a child. At this time, we do not know the identity of the child, but it is speculated that the main killer and the child are the same person.