N K Sakthivel, Vice-Principal of the Nehru College of Engineering, was arrested from a relative's farmhouse at Annoor after the latter's mobile phone signals were tracked, police said.
He is being brought to Thrissur police club, they said.
There are a total of five accused in the case.
Nehru Group of Institutions Chairman P Krishnadas and a college official Sajith, son of former Congress minister, K P Vishwanathan, were arrested earlier.
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Jishnu Pranoy, a first year student of Nehru College of Engineering in Thrissur, was found hanging in the college hostel in January last, following alleged harassment by college authorities.
Chief Minister Pinarayi Vijayan said in Thrissur that his government and police would everything they can to bring all the guilty to book in the case.
"The government will take all steps to get justice for Jishnu's family," he said speaking at a function at Irinjalakuda in Thrissur district.
The CPI(M)-led LDF government had on April 6 set up a Special Investigation Team to nab the absconding accused in the suicide of Jishnu and had announced a Rs one lakh reward to those giving information about the two wanted men.
The government had come under flak from various quarters, including LDF partner CPI, for the "high handed" police action against the mother of Jishnu and others.
As a mark of protest over the police "highhandedness" against Jishnu's family, a state-wide hartal was observed on April 6 in response to a call by the Congress-led UDF and the BJP.
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