Updated: 02/17/2007 - Utility officials are saying.. they now know what caused the natural gas leak in the state capitol yesterday.. Even though the building is heated by steam. A madison gas and electric spokesman, says that the leak came from a natural gas coupling under a street less than a block from the building, and next to a telephone conduit that went into the capitol. The building was evacuated yesterday.. after a faint natural gas odor was reported in teh basement. Governor doyle was not in the building..