A special National Investigation Agency (NIA) court in Kochi on Thursday convicted 13 people in connection with the attack on a college professor for preparing a question paper that allegedly contained blasphemous references against Prophet Mohammed.
However, the court acquitted 18 others for want of evidence five years after the attack.
A lecturer of Malayalam literature at Newman College in Thodupuzha, TJ Joseph was allegedly attacked by activists of the Popular Front of India in July 2010 and the palm of his right hand was chopped off as he was returning home from church with his mother and sister in Ernakulam district's Muvattupuzha.
The attackers told him that he was being punished for the sacrilegious undertones of one of the questions he had framed.
Joseph on bail when he was attacked. He was arrested in April 2010 over the question that some Muslim groups claimed included an insulting reference to the Prophet.
Despite widespread condemnation the incident evoked, the college dismissed Joseph from his job for breach of discipline while he was recuperating in a hospital. Later, his wife committed suicide forcing the college authorities to take him back.
A court had given him a clean chit in the case registered against him for hurting religious sentiments.
The quantum of punishment will be pronounced on May 5. Five others in the case, including the first accused, are absconding.
According to the prosecution, the attack was planned and carried out in retaliation to preparing the question paper for second year B Com students.
Reacting to the verdict, Joseph said he had pardoned his attackers long back.
"More than the attack, the attitude of authorities pained me well," he said.
This is one of the first cases being probed by the NIA in Kerala.