Tests on material taken from the barn where a flash fire killed three horses the evening of June 22 at Belmont Park have come back negative for flammable accelerants, a source at the Nassau County Bomb and Arson Squad said yesterday. Investigators had raised the specter of possible arson the day after the blaze.

“We have a suspicious fire because it was fast-spreading,” said the source. “But there was hay in the stalls and cross-ventilation, and that can burn quickly. Even the green alfalfa can combust spontaneously. We have no suspects, no motive and no witnesses.”

Veteran horseman James Toner, who trained the three horses, said all along he found arson an unlikely cause.

“I still find it hard to believe anyone who works around horses would do something of that horrific nature,” he said.