A court in Finland has convicted a man and a woman of plotting to kill dozens of people at the country's largest university and sentenced them to at least three years each in prison.

In its Friday verdict, the Helsinki Regional Court found the pair, both aged 24, guilty of possessing weapons, ammunition and chemicals meant "for the mass murder of at least 50 people, chosen randomly." They also planned to rob a gun store to increase their arsenal for the attack, the court said.

It sentenced Nita-Minttu Tirkkonen to three years in prison and gave Josef Andrei Hannu a 37-month prison term, including for the possession of child pornography.

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Court papers described how the disillusioned pair met over the Internet in 2012, discussed their hatred toward society and exchanged details about mass murders in encrypted emails. During the course of some 15 months, they plotted to slaughter people at the University of Helsinki in early 2014.

Hannu told the court he had been bullied at school and started thinking about an attack after two school shootings in 2007 and 2008 in Finland that killed 20 people. He also had images of last year's Boston Marathon bombings on his computer.

After their first meeting in January, which included a visit to the university, Hannu travelled back to his home in northern Finland and decided to postpone the attack, apparently to prepare for it more carefully. But Hannu told the court he had decided to call it off but was afraid of losing Tirkkonen's trust and could not tell her.

The plot was discovered when Hannu tried to recruit a 17-year-old girl into the plot but she told another person, who tipped off police.

The defendants gave no clear motive for their actions but the court found they were prompted by feelings of hatred toward society, anger and revenge, including for being teased.

Both pleaded innocent to the charges, saying the attack was never meant to be carried out.

It was not immediately clear if they would appeal.