An Indian court on Tuesday found a Bangladeshi man guilty of raping an elderly nun in a crime that sparked an outpouring of anger at persistently high levels of sexual assault in the country.

The 71-year-old nun needed surgery after the brutal attack in 2015, when a gang of robbers broke into the convent school where she lived in the eastern state of West Bengal.

A court in the state capital Kolkata found Nazrul Islam guilty of rape and attempted murder, among other offences.

“It was a shameful act,” additional judge Kumkum Singha told the packed City Sessions Court.

Singha said Nazrul Islam acted alone in raping the nun, adding that five others arrested for their involvement were charged with offences unrelated to the sexual assault.

Islam will be sentenced on Wednesday.

The nun, who cannot be named for legal reasons, was attacked after the robbers ransacked the Convent of Jesus and Mary in Ranaghat and stole cash and other items. A holy scripture was also torn and a statue of Jesus was broken.

The assault was the latest in a string of high-profile rapes in India, and prompted much soul-searching as priests and schoolgirls took to the streets demanding justice for the “inhuman” crime.

Supporters closed shops, shuttered schools and held candlelit vigils outside the hospital where the nun underwent surgery for injuries suffered during the attack.

The police came under fire for perceived inaction after 10 men were detained but no arrests made, despite the faces of some attackers being captured on CCTV footage. It took three months before the main accused was arrested.

Indian government's data for 2015 shows 34,651 rapes were recorded but campaigners say the true figure is likely to be much higher given the social stigma that still surrounds such cases.

India strengthened its laws on sexual violence after the fatal gang-rape of a Delhi student five years ago caused global outrage, but attacks remain widespread and enforcement is patchy.

The crime also sent shockwaves through India's small Christian community, which was already reeling from a series of attacks on churches in the months before the assault. The trial was relocated to Kolkata at the request of the assaulted nun, who expressed fear for her safety in Ranaghat where the crime occurred.

Indian Prime Minister Narendra Modi, a Hindu nationalist, expressed deep concern over the attack but was criticised for not speaking out earlier against religious violence.