A high school student accused of spraying his principal with blue and green silly string is off the hook, after a San Francisco judge declared a mistrial Thursday, reports the Associated Press. Jurors deliberated for three hours but couldn’t reach a verdict on assault charges against Steven Babb, now 19. He stood accused of spraying his former Vintage High School dean Andrew Herron with the silly string during commencement exercises. Babb said he was simply reveling in the post-commencement atmosphere. He said he later apologized to Herron “for any embarrassment or injury but not for the act itself.” Prosecutors described it as a sustained, point-blank attack. “(Babb) directed the stream of one can up his nose and another at his eyes,” Prosecutor Gary Lieberstein said, adding that he believed Babb’s conduct was immature but said his office would drop the case. “There are certainly more serious cases than this,” he said.