Wisconsin Gov. Scott Walker is expressing his condolences to the family of a firefighter killed in a massive natural gas explosion. Authorities say a contractor ruptured a natural gas line in downtown Sun Prairie on Tuesday evening. The gas somehow ignited, leading to an explosion that leveled half a city block and claimed the life of 34-year-old Sun Prairie Fire Department Capt. Cory Barr. He leaves behind a wife and twin 3-year-old girls. Walker toured the rubble Wednesday evening and spoke at a news conference in a city park. He offered his love and prayers to Barr’s family and children. He also praised firefighters and police who evacuated dozens of people from the area before the explosion. Sun Prairie police Lt. Kevin Konopacki said authorities are in the midst of an in-depth investigation to determine how the line was ruptured and what sparked the explosion.