The scuffle between Nay Myo Lin and the police officer broke out after the officer, standing in the middle of a moving motorcade, knocked a man off a motorbike, Thein Than Oo, the defense lawyer, told Reuters and a witness video showed.
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A group of students organized a march on Myanmar's largest city, Yangon, last year in March in protest against an education bill they said would stifle academic freedom.
It was brutally broken up by police before reaching its destination, with riot squads charging people with batons. Many student activists are still on trial.
"It's not fair at all to charge me under Section 332 after ignoring the policeman's unjust act of pulling down the motorcycle of a protesting student," Nay Myo Lin told local media after the verdict, referring to the section of the penal code under which he was sentenced.
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"I didn't mean to hurt that policeman. I just tried to give protection to a citizen who was being treated unjustly in my presence," said the reporter, adding that "the police must have applied pressure on the court" to pass a three-month sentence.
Police Colonel Zaw Khin Aung from the Naypyitaw-based Myanmar Police Headquarters rejected the allegations.
"It's quite impossible for the police to influence the court. It’s just up to the judge to lead the hearing and to make the final decision on the judgment," said the Zaw Khin Aung.
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Both police and the judiciary are overseen by Myanmar's Home Ministry, which is directly controlled by the armed forces.
Thein Than Oo, the lawyer, said he was planning to appeal.
Yangon-based BBC reporter Jonah Fisher confirmed the arrest on his official Twitter account, but added that BBC Myanmar was not in a position to comment on the matter.
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