What can I do about a landlord accusing me of causing a Leak in the building.

I live on the third floor of a building ontop a business. A flood was in the business first floor. The landlord automatically accused me of negligence and said the leak came from my apt when he did not inspect mine or the 2nd floor apartment. He also stated the 2nd floor apt suffered damages which was not true. I spoke to my neighbor and she said no such damage happened. We both received a letter from the real estate saying we are responsible for the flood in the business and that we will have to pay. No plumber has come to investigate the source of the leak. I checked my apartment and found no leaky faucets or malfunctions of any kind. I suspect that if there is a leak, it must be within the walls of our very old building. Would I, the tenant or the landlord be accountable for this?