A fourth victim died early on Wednesday as a result of a kerosene attack by an island man on his family during a New Year's dinner.
Jesus Sanchez, 28, a nephew of the alleged attacker, died Tuesday night, according to Puerto Rico Medical Center Director Ernesto Torres.
The alleged attacker's mother, Josefina Diaz, as well as a 32-year-old cousin, Samuel Molina Sanchez, and a 17-year-old niece, Pamela Sanchez Vazquez, had died earlier from burns suffered during the attack.
Sanchez's 25-year-old fiancee, Kate Donahue of Seattle, was seriously hurt in the attack and was flown to the United States on Wednesday morning in an air ambulance to receive special treatment.
"The prognosis of this woman is very poor," Torres said during a morning radio interview. "The young woman, like the other youth Jesus, has burns over 90 percent of her body, which is not compatible with life."
The alleged attacker, 45-year-old Justino Sanchez Diaz, lived with his parents and sister at the home in the Puerto Rican town of Florida where the attack occurred.
Police said Sanchez Diaz doused the walls of the home with gasoline and hid fuel-filled canisters under furniture in the dining room where the dinner was to take place.
When it began, Sanchez Diaz allegedly spilled kerosene over the guests and set them on fire with a fuel soaked stick, according to police.
Police have no clear motive and say Sanchez Diaz has declined to talk with authorities.
Sanchez Diaz has been charged in relation to three deaths and is in jail after being unable to post bail that now amounts to more than $3.5 million.
