The six will be formally charged in court on Thursday on accusations that they kidnapped, gang-raped and murdered the 23-year-old woman on a moving bus in the capital New Delhi on December 16, police spokesman Rajan Bhagat told reporters.
Media reports say some 30 witnesses have been gathered, and the charges have been detailed in a document running into more than 1,000 pages.
Outraged Indians have been demanding the death penalty for the six men, holding demonstrations almost every day since the rape. Murder is punishable by death and rape by life imprisonment. But juveniles - those below 18 years of age - cannot be prosecuted for murder.
Another police officer said a bone test is being conducted to determine if the youngest suspect in the case is indeed a juvenile. If the test determines he is 18 years or older he will be treated as a legal adult, said the officer, who spoke on condition of anonymity because he was not authorized to disclose sensitive information.
The brutality of this case has made Indians confront the reality that sexual violence is deeply entrenched in the society. Women face daily harassment, from catcalls on streets and groping in buses to rapes. Often police refuse to accept complaints by victims and even blame them for inviting unwanted male attention by dressing provocatively. Families too dissuade victims from coming forward in the belief that it will ruin their reputations.
Activists hope that the savage assault on the young woman, a physiotherapy student, will shake off the taboo associated with sexual violence and make the authorities take such cases more seriously.
The young woman and a male companion were attacked when they got into an off-duty bus in southern New Delhi to go back home. The six men, including the bus driver, took turns to rape her and beat her with an iron bar which they also inserted in her body causing severe injuries to her organs.
The woman, who has not been identified, was airlifted to Singapore for emergency treatment but died on Saturday. She was cremated in New Delhi on Sunday, and the ashes were to be submerged in the holy river Ganges near her hometown in the northern Uttar Pradesh state in accordance with Hindu customs.
Protesters and politicians from across the spectrum called for a special session of Parliament to pass new laws to increase punishments for rapists - including possible chemical castration - and to set up fast-track courts to deal with rape cases within 90 days.
Thousands of Indians have lit candles, held prayer meetings and marched through various cities and towns to express their grief and demand stronger protection for women and the death penalty for rape, which is now punishable by a maximum of life imprisonment. The protests continued on Tuesday.
On Monday, the Indian army and navy canceled their New Year's Eve celebrations, as did Sonia Gandhi, head of the ruling Congress party. Several hotels and clubs across the capital also did not hold their usual parties.