I thought the killer was Gwen - from the beginning. Turned out to be Jamie, just one off, though the real twist was that although Jamie beat Rosie, he was not the one who put her into the water in the trunk of the campaign car, where she died.
That was be Terry, who (of course) did not know the girl in trunk was Rosie, presumably didn't hear her screams, which we the audience did, in one of the best scenes of a series brimming with great scenes. We also now understand why Terry was devoting her life to the Larson family after Mitch took her vacation.
All of that makes powerful sense. What doesn't is the extraordinary coincidence that Terry, involved with Ames, would get into that position where she unknowingly drove her niece into the water. A bridge too far.
But the Larsons were presented perfectly after that, finally beginning to be a little on top of their heartbreak, watching the movie that Rosie had made about her life and aspirations. That was a twist, too - Jamie really had nothing to fear from that movie, no reason to accost Rosie in the casino.
Linden and Holder ended well, too. One of the best exchanges - Holden says we got the bad guy, and Linden responds, who would that be? No single bad guy in this story, just lots of people who contributed with their errors and ambitions and insecurities to Rosie's death.
No word, as yet, on whether The Killing is coming back. I sure hope it does - it's among the best detective shows of all time, second to none in the sensitivity with which it handled the impact of the murder on both the family and the cops investigating the crime. It's a story I'll never forget.
See also The Killing Season Two Premiere ... The Killing 2.2: Holder ... The Killing 2.11: Circling Back
And see also The Killing on AMC and The Killing 1.3: Early Suspects ... The Killing 1.5: Memorable Moments ... The Killing 1.6: The Teacher ... The Killing 1.8: The Teacher, Again ... The Killing 1.9: The Teacher as Victim, Again ... The Killing 1.10: Running Out of Suspects ... The Killing 1.11: Rosie's Missing - from the Story ... The Killing 1.12: Is Orpheus the Killer? ... The Killing 1.13: Stretching Television