In the first season of "Riverdale," it is revealed that Jason Blossom was killed by his own father, Clifford Blossom. The murder of Jason Blossom is the central mystery that drives much of the plot in the early episodes of the series.
Throughout the season, the characters, especially Betty Cooper and Jughead Jones, investigate the circumstances surrounding Jason's death, trying to uncover the truth behind the tragic event. Various suspects are considered, and the mystery unfolds with twists and turns, but ultimately, it is revealed that Clifford Blossom, the head of the Blossom family, was responsible for his son's death.
Clifford's motive for killing Jason is connected to a series of dark secrets and criminal activities involving the Blossom family's maple syrup business and ties to organized crime in Riverdale. The revelation of the true killer marks a turning point in the first season's storyline and has significant implications for the characters' relationships and the town's dynamics.