Two years after a natural gas-fueled explosion rocked downtown Canton, Illinois, killing one person and injuring 11 others, the National Transportation Safety Board (NTSB) has concluded its investigation into the incident.

The November 16, 2016 natural gas release and subsequent explosion occurred while utility workers were trying to fix a gas leak that a contractor caused while digging, according to news sources. Killed in the blast was 38-year-old Arturo Silva Jr., an employee of Ameren Illinois, a power company. Three other workers were injured.

The NTSB has determined that the probable cause of the incident was third party damage from Sure Shot’s directional drilling to install underground fiber optic conduit. Contributing to the pipeline damage was Sure Shot’s decision not to excavate at the utility crossing to visually inspect the work, while in progress, until clear of the underground utilities, as required by Illinois law.

Making things worse: the failure of Sure Shot and Ameren to evacuate the area.