Authorities said during a Thursday news conference that they believe Itzcoatl Ocampo was involved in the murders of a Yorba Linda woman and son in October.
Police said they have "significant evidence" that links Ocampo to the double homicide.
Raquel Estrada, 53, and her son Juan Herrera, 34, were found stabbed to death inside their home. Estrada's 24-year-old son, Eder Herrera, was arrested and charged with killing his mother and brother.
Officials said they are not yet dismissing the charges against Herrera at this time because he may have still been involved.
Anaheim Police Lt. Julian Harvey said there is an association between Ocampo and Herrera, but he didn't specify the nature of the association.
The former Marine lived a mile away from the family. Ocampo's proximity and the similarity of all the murders are key factors in the investigation.
The Associated Press contributed to this story.