By the end of the season, we learn that Alex is actually to blame for Bryce's death, though Monty is framed for the murder instead. Deputy Standall feels pretty confident that his son is the guilty party, but he still accepts the story about Monty. Later, when he tells Alex that Monty is being named as the killer, Alex's relieved reaction leaves no room for doubt. Standall burns Bryce's tape and the clothes Alex wore when he killed Bryce to make sure that all of the evidence is destroyed.
Alex may have committed the crime, but Jessica watched it all go down without doing anything, making her complicit. We learn that, on the night of Bryce's murder, Jess calls Alex after she can't get a hold of Justin and has him accompany her down to the pier to meet up with Bryce. At the pier, Bryce gives Jess a tape he made with his confession, as well as an apology for everything he did. Though Jess wants to leave after receiving the tape, Alex attempts to help Bryce up, which only angers Bryce. Alex pushes him into the water, where he drowns, and Jess tells Alex that they have to stay apart to make sure they never get caught. However, once Alex is cleared of the crime, we see Jess join the Standalls for Thanksgiving, so it seems these two might be OK after all.