Five months after an explosion leveled three rowhomes and killed two people in Baltimore, Fire Chief Niles R. Ford has provided a cause.

Two people were killed and seven people were injured after three rowhomes exploded on Labyrinth Road in northwest Baltimore in August. Ford reported Tuesday that the explosion was a result of a buildup of natural gas.

Ford reports that on Aug. 9, one day before the explosion, unpermitted HVAC work was being done in the basement of 4232 Labyrinth Road. A buildup of natural gas formed, which was found to be spiked on four gas meters between 1:30 a.m. to 2 a.m. on Aug. 10.

Ford says on the morning of Aug. 10, a stove was lit, igniting the explosion.

Ford clarified that the contractor was licensed, but no proper permits have been found for that address.