The sixth suspect in the case that has outraged the country is under 18 and a juvenile.
Police ordered a bone test for the sixth accused to confirm his age, according to a police officer who spoke on condition of anonymity as he was not authorised to talk to reporters.
Under Indian law, a juvenile cannot be prosecuted for murder.
New Delhi police spokesperson Rajan Bhagat said on Tuesday that a charge-sheet in the case will be filed in court on Thursday. The suspects face the death penalty if convicted.
The 23-year-old physiotherapy student died last week in a Singapore hospital where she had been sent for emergency treatment after the crime in India's capital on December 16. The case has triggered protests across India and raised questions about lax attitudes by police toward sexual crimes.
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.
On Monday, the Indian army and navy cancelled their New Year's 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.
Women face daily harassment across India, including catcalls on the streets and groping and touching on public transport. – Sapa-AP