Cesar Altieri Sayoc Jr. was taken into custody in Florida on Friday.
The 48-year-old from Plymouth suffered severe injuries.
Nearly 30 reports of vandalism to homes and vehicles.
The Hennepin County Sheriff is investigating.
Medical examiners released their identities on Sunday.
The fire started in the art room, the school says.
The child found a loaded handgun and died in an accidental shooting.
Police are investigating the situation.