(AP) -- A house explosion in the Bronx that killed a fire battalion chief may have been caused by a tampered gas main.

At a graduation for new police officers Thursday, New York Police Department Commissioner James O'Neill told Newsday the tampered gas main leaked then sparked, causing the Tuesday blast that killed Chief Michael Fahy.

Authorities are looking into whether the building was used to grow marijuana.

A Manhattan resident, Garivaldi Castillo, has been arrested on criminal possession of marijuana charges. His lawyer has questioned the evidence linking him to the house.

At a court hearing Thursday, prosecutors said the home had been tightly sealed with insulation to keep the plants warm. They said there were also bins of fertilizer.

Police are also questioning another man for possible ties to the explosion.