Residents returned home this weekend in Teutopolis after an anhydrous ammonia spill and accident killed five people.
 

Now the National Transportation Safety Board has launched an investigation into the accident that turned deadly and drove hundreds from their homes.

The NTSB says they are interested in the safety aspect of the crash. Tom Chapman, an NTSB Board Member, says the driver of the tractor trailer carrying the chemical may have been trying to avoid an accident.

Chapman says NTSB investigators will be on scene for four to six days.