The National Transportation Safety Board has released its initial findings into what led to last month’s house explosion in Lexington that killed a five-year-old boy and seriously injured his father and older sister.

According to the board’s preliminary report into the explosion the evening of April 9, a drilling subcontractor installing a fiber optic line near 18th and Franklin struck a four-inch polyethylene pipe containing pressurized natural gas just after 4 p.m. The subcontractor alerted the Lexington Fire Department and pipeline owner Liberty Utilities.  First responders arrived around 4:20 p.m., while utility crews arrived 20 minutes later to begin isolating the leak. The utility coordinated the evacuation of a nearby business but not residences that were at least 80 feet away from the leak. The home explosion occurred at around 7:42 p.m., and the damaged main was isolated 30 minutes later.

The NTSB’s initial findings suggest that the subcontractor Alfra Construction had called Missouri 811 five days before the accident to have underground utilities in the area marked. Liberty Utilities reported all their utilities as being marked on April 7; however, the NTSB says that the location of the gas main section involved, “was not identified or marked during this process.” The NTSB adds that their investigation continues, with an expected focus on Liberty Utilities’ responses to 811 requests, leak and repair history, record keeping, and emergency response and isolation procedures, among other issues. The NTSB says they’ll also review local emergency response and evacuation procedures.

The explosion April 9 claimed the life of five-year-old Alistair Lamb. His father Jacob Cunningham filed a wrongful death lawsuit last month in Lafayette County Circuit Court against Liberty Utilities and three companies involved in the installation of the fiber-optic cable, seeking damages.