A statement from the U.S. island's justice department Tuesday also says that Justino Sanchez Diaz has been charged with a sixth count of murder. That charge stems from the death of a hospitalized victim Jan. 29.
Also among the dead are the suspect's elderly mother, a nephew and the nephew's fiance from Seattle.
Police allege Sanchez doused family members with gasoline when they sat down for dinner and set them on fire.
It is unclear if Sanchez has entered a plea in the case. Defense attorney Luis Gonzalez did not return calls for comment.