The 71-year-old nun was raped after a group of seven men broke into a convent school, the police said. They vandalized the school before the nun was sexually assaulted.
The man who raped the nun is a 28-year-old Bangladeshi national, Nazrul Islam or Noju, who had been arrested after he was identified by the nun from a line-up of suspects presented to her by the police.
Five other men who were with him have been convicted of conspiracy and dacoity. One of the suspects is missing.
Of the six men convicted today, five are Bangladeshis who crossed the border in March 2015 and then attacked a co-ed school run by missionaries at Ranaghat, 80 km from Kolkata. The sixth is a resident of Habra in the North 24 Parganas district. He had conspired with the others at his home to hatch the plot to rob the convent.
Around 2.30 am, the men entered the convent attached to the school and were looting valuables from the chapel when the sisters raised an alarm. The senior-most nun tried to stop them; she was raped after the others were locked up in a different room.
The attackers fled at dawn with cash worth 12 lakhs.
The incident drew global condemnation. A police post was located just 100 metres from the convent but cops were not patrolling the area and came to know of the crime only when the sisters raised an alarm.
Chief Minister Mamata Banerjee, too, had condemned the incident and ordered a probe by the Criminal Investigation Department of the state police (CID). But when she tried to visit Ranaghat, angry mobs blocked her convoy for about an hour. She later met the nun in hospital.
Based on CCTV footage that was available, the police arrested four of the suspects in Ludhiana. Two others were picked up at a train station in Kolkata three months later, among them, the leader of the criminal gang who also raped the nun.