None other than Nico!
Except we have only Nico's brother's word for it, and let's face it, he's not the most reliable witness, is he. And revealing a true killer in the last few minutes of an episode, which is not even the finale, smacks of false lead or red herring to me.
Not to mention that Nico doesn't seems like a killer. His brother says he's mean when he's drunk, but that means he's a killer? I doubt it. Not that it wouldn't be one powerful twist if he were the killer, but I just don't believe it.
Also - the husband, Tom, was shown point blank talking on the phone with the two bad guys who presumably were out to kill Laura and Nico, and certainly risk Serena's life, so he seems like more of a villain than even last week, when I said I couldn't quite see him harming his daughter. I guess we don't know for a fact what that pair straight out of Pulp Fiction were really out to do - maybe not kill or even hurt anybody - but they sure were giving a pretty good impression of would-be killers throughout the episode.
The voice over at the end said that Nico and Laura were quickly approaching their fate in the water. This series is still managing to be somewhat interesting, even though the narrative is a klunky and there hasn't been much if any time travel in the past few episodes.
See you back here a little closer to fate next week.