- Nun was trying to prevent six men from robbing the Christian school
- Gang believed to have gagged security guard before violent rampage
- CCTV footage released shows suspects leaving the school's staff room
- Five others have been detained for questioning, police said
- Latest in a series of violent gang-rapes that has shocked the country
Arnab Ghosh, a police superintendent, said: 'CCTV footage showed that six men, aged between 20 and 30, scaled the boundary wall around 11.40 pm and entered the school and disconnected the telephone lines.'
The robbers then tied up and gagged a security guard before entering the nuns' room, where they found the women sleeping, police said.
Mr Ghosh added: 'At least two of them were armed and the rest were carrying burglary tools. In the chapel, a holy scripture was found torn and a bust of Jesus was broken.'
The nun is recovering in hospital in Ranaghat.
Furious residents took to the streets yesterday, shouting slogans demanding action and blocking off the main highway.
Mamata Banerjee, West Bengal Chief Minister, also tweeted her condemnation of what she called a 'horrific attack', promising 'swift, strong action'.
Archbishop Thomas D'Souza has appealed to people to maintain peace and harmony in the area.
He said: 'In our Sunday Mass, we prayed for the sister to recover quickly from trauma, fear and her physical injuries. We will pray for her again this evening.
'They not only committed a heinous crime, but they also vandalized the chapel. This is the first time such an attack has happened in India.'
The incident comes at a time of heightened sensitivity over women's safety in India, which last week saw a documentary about the 2012 gang-rape of a student in Delhi being banned.
Authorities said screening the documentary could have caused public disorder, but critics accused the government of being more concerned with the country's reputation than the safety of its women.
Shocking footage also emerged this week of an angry mob stripping and slowly beating a man to death in an Indian village after he was accused of raping and murdering an 11-year-old girl. The prolonged attack on the 18-year-old was watched by a jeering 1,000-strong crowd. [Shocking? Why? Posse or vigilante justice is what happens when the structures put in place to enforce laws fail to protect innocent citizens and often overlook crimes such as rape. I hope it was a large crowd of women who executed justice against the rapist.]