A fatal explosion last month in downtown Kansas City, Missouri, was caused by the accidental ignition of natural gas vapors that had accumulated inside a popular restaurant, according to a report from a joint city-federal task force.

After a gas line nearby was ruptured, firefighters asked employees at JJ's restaurant "to put the flames out on the candles, stove and hot water heater" inside, said the report.

When queried after the blast by investigators, the restaurant's manager acknowledged the initial request and said workers "only put the candles out and turned the stove off, but did not turn out the pilot lights for the stove or hot water heater," according to the report issued Wednesday.