Sherman Sanders died Friday after a week in the burn center at the University of South Alabama in Mobile. He had suffered third-degree burns over more than half of his body.
Investigators said his wife, Edna May Sanders, 45, fled their home in Diamondhead with their two children on July 28.
Police believe she heated about two quarts of household cooking oil on the stove, allowing it to reach a simmer before pouring it over her husband's head, chest and arms.
Authorities have said they were unsure what led to the assault. The couple had been married only a short time.
FBI Special Agent Jason Pack confirmed that federal authorities will help the Hancock County Sheriff's Department search for Edna Sanders because she may have crossed state lines.
"She has family in Texas and Louisiana, and that's where we are concentrating all our efforts right now," said Kenny Hurt, the county's chief investigator.