Ten of the 13 have been have been found guilty under various sections of the central law dealing with terror-- the Unlawful Activities (Prevention) Act (UAPA).
The court, which posted the matter to May 5, is likely to pronounce the quantum of punishment on the same day after hearing.
Eighteen people have been acquitted by the Special NIA court Judge P Sasidharan citing lack of evidence against them in the case.
Besides UAPA, the court has also found the 10 accused guilty under various sections of Explosive Substances Act and IPC that deals with criminal conspiracy and attempt to murder.
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The court, however, convicted three accused--Abdul Lateef, Anwar Sadique and Riyas-- under Section 212 of IPC. dealing with harbouring offenders.
They did it out of enmity towards Joseph accusing him of hurting religious sentiments of a community through a question paper he set for his students.
The court, which began the trial of the case in July 2013, had examined over 300 prosecution witnesses, four defence witnesses, over 950 prosecution documents, nearly 30 defence documents, and over 200 material objects.
Thirty-seven persons were charge-sheeted by the NIA in the case. However, 31 only underwent trial as the remaining six, including first accused Savad were absconding.
According to the police which initially probed the case, the accused wanted to kill Joseph for derogatory religious remarks in a question paper he set for B.Com semester examination in the Newman College.