However, they are seeking the public's help in identifying a man who was seen in the area of the fire moments before the fire was discovered, the fire department said in a news release.
Asked if they are still investigating the possibility of arson, assistant chief Erich Scheunemann said only that the man was "a person of interest."
Scheunemann said investigators have completed their examination of the fire scene.
The fire started in a detached garage and spread to a duplex and the float, which was in a car tent in front of the garage.
Investigators found the area where the fire started but not the exact point of origin because of "extensive damage," the department news release said. Without a point of origin, they couldn't figure out the cause.
The day of the fire, a department spokeswoman said it was being called suspicious and was under investigation.
Michael Richardson, president of the Imperial Court, said the group rallied after the float was destroyed two days before the Fourth of July parade. They built another -- "the fastest float that was ever built" -- and won the top prize in the parade.
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