Police say there's now substantial evidence the Bronx house that exploded and killed a firefighter was a marijuana grow lab.
They say investigators found botanical fertilizers on the second floor of the building.
Battalion Chief Michael Fahy was killed by flying debris while directing traffic outside the home last Tuesday.
Police say they believe a gas leak led to the deadly explosion, but are still trying to pinpoint the cause.
"We excavated, or we are excavating, the pipe that goes into the house. We found a deviation within the home in the basement that we can't explain right now, so we're going to take that out, extract that piping and its fittings, and send it down to Maryland to the ATF lab to see what kind of construction went into it, how long it's been there and to see if that's the issue," said NYPD Chief of Detectives Robert Boyce.
Two men are under arrest in connection with the explosion.
Julio Salcedo was extradited from New Jersey Friday and is charged with felony possession of marijuana.
Garivaldi Castillo is also facing possession of marijuana charges.