Well I’m sure the pilot was watching the gas gauge, and very likely the chopper has a low fuel warning light and warning sound. So if it ran out of fuel, which is not impossible, it wouldn’t be because of circling for a while over downtown. It would be caused by a failure of the gas gauge and low-fuel warning system. The NTSB will look at all possible causes, I’m sure. Running out of fuel, or defective fuel containing water or some other substance, are two of many possibilities. If it’s technically possible, I’m sure they’ll determine whether the pilot was incapacitated by a heart attack or some other medical problem.
The fire wouldn’t have spread over a quarter acre without fuel...doubt it ran out of fuel. They will find out the cause.