The NTSB's investigation into the crash is ongoing.
Tests shows an unusually high concentraion of natural gas in the soil in and around the explosion site.
The National Transportation Safety Board vows to discover the cause of the building explosion.
Investigators said the Seastreak ferry captain tried to slow the boat but it would not go into reverse.
Investigators are looking into whether a mechanical mishap led to Wednesday's crash that left 57 hurt.
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