Federal authorities joined the investigation Thursday into a natural gas explosion at a US school that killed two adults and sent students fleeing as a building partially collapsed.
Rescuers pulled the body of the final missing person from the rubble late Wednesday at a Minnesota private Christian school. Two people were killed, a school janitor and a receptionist.
All students at Minnehaha Academy were accounted for, some fleeing the building at the school for grades kindergarten to 12 just moments before the explosion.
Nine people were injured. Three remained in the hospital Thursday, one in critical condition, according to the Hennepin County Medical Center.
"This morning our prayers are with Minnehaha's facilities team member Bryan Duffey and his family. We pray for his healing and for the wisdom of the doctors and nurses caring for him at this time," the school said in a statement.
The National Transportation Safety Board (NTSB), known for investigating plane and train crashes, sent an investigative team to the school.
"The NTSB investigates pipeline incidents and accidents," agency spokesman Christopher O'Neil told AFP.
The natural gas explosion occurred Wednesday morning in the center part of one of the school campus buildings in the city of Minneapolis, where a construction crew was working.
The blast pushed part of the building's wall outwards, causing the roof to collapse and pancaking two floors into rubble, according to fire chief John Fruetel.
School receptionist Ruth Berg and janitor John Carlson were killed. Rescuers recovered their bodies from the rubble hours after the explosion.
Witnesses told the Minneapolis Star Tribune newspaper that someone warned of a gas leak moments before the explosion.
The few students in the building -- school is currently not in session -- managed to escape the blast, according to the newspaper.
"All the windows just kind of burst out, and there was a huge explosion that was so loud it kind of shook your insides," student Kylee Kassebaum told the Star Tribune.