The body of 25-year-old Brittany-Jane Royal was found in the water off Kalapana in May 2013. The native of Tustin had recently moved to Hawaii.
Detectives said at a news conference on Monday that Royal was strangled by her boyfriend, 22-year-old Boaz David Johnson, during a domestic dispute.
Police searched for Johnson after a grand jury indicted him on second-degree murder last month. But on Jan. 2, his body was found hanging from a tree.
In a handwritten suicide note, which was found near his body, Johnson confessed that he strangled Royal and threw her body in the ocean, according to investigators.