Gregory F. Sullivan was showing students a documentary when he said: "If someone with orange hair appears in the corner of the room, run for the exit."
Colorado shooting suspect James Holmes has dyed bright orange hair.
The professor had just turned down the lights when he made the remark.
The father of one of his students was among the 12 people killed in the July 20 shooting.
The New York Times reports Long Island school said the decision to suspend Sullivan was made after careful review of all information.
Sullivan has apologized for the remark.
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