Two people were killed after a wall collapsed at a Hendersonville construction site Thursday morning, while one other was injured. The accident occurred in the 200 block of Indian Lake Boulevard just before 10:30 a.m. Twenty-four-year-old Joel Muniz and Jose Velasco-Sanagustin, 37, were killed at the scene. Jeff Costello, 44, of Scottsville, Kentucky was airlifted to Vanderbilt University Medical Center. He is reported to be in stable condition.Officials said it remains unknown what caused the wall, which was 25 feet high and 200 feet long, to fall. "Only thing we know right now is the wall fell. We don't know what caused the wall to fall. We don't know what actions were being done precisely at that time," Detective Jim Vaughn said. Emergency responders from Hendersonville, Goodlettsville, Gallatin and Metro all responded to the scene. Tammy Taylor told Nashville's News 2 her fiancé, Tony was working at the site when the accident occurred. He was not injured in the incident. "I was worrying. [I was a] nervous, nervous wreck," she said. The incident remains under investigation.