Three accused Mukesh, Pawan and Vinay were on Wedesday produced in court where they confessed to the crime.
Pawan refuses to undergo test identification parade saying he committed a "heinous act."
Mukesh agrees to undergo test identification parade by victim's male friend, the TIP will take place on Thursday in Tihar Jail.
Vinay reportedly refused to undergo test identification parade and said before the court that he assaulted the boy, not the girl.
Pawan and Vinay have been sent to four-day police custody while Mukesh sent to Tihar jail for 14 days in judicial custody.
A fifth accused, Akshay Thakur has been detained from Aurangabad in Bihar and is being brought to Delhi, sources said.
Water canons were used on protesters who had gathered outsite Delhi chief minister Shiela Dikshit's residence on Wednesday, to demand immediate action in the gangrape.
PM say incident 'upsetting'
Prime Minister Manmohan Singh described the incident as "very upsetting". He directed Home Minister Sushilkumar Shinde to ensure that culprits are brought to book and such incidents are not repeated.
"It's a heinous crime...it is very upsetting," he said.
In Parliament, Shinde said that there will be an immediate crackdown on buses having tinted glass and heavy curtains. They shall be impounded immediately, if they do not remove them.
All buses will be asked to keep their lights on while plying at night in Delhi and these must be parked with their owners and not their drivers, Shinde told Rajya Sabha.
Three days after a 23-year old woman was assaulted and gangraped in a moving bus in the national capital, she continues to fight for life in Safdarjung Hospital.
According to TV reports, vital organs of the girl are permanently damaged.
She is on a ventilator in the hospital's ICU and is getting a regular infusion of morphine to control the pain, doctors treating her claim that the pain is so excruciating that despite the morphine dose she is conscious.
But the victim, despite her critical injuries, is putting up a good fight.
The victim had received severe genital and abdominal injuries and lost a lot of blood during the assault. Doctors claimed that they had never seen such brutal assault.
"Her condition is critical but she is conscious and communicating by writing notes. She is a spirited girl and is showing tremendous will to fight her condition," said Dr BD Athani, Medical Superintendent, Safdarjung Hospital.
To boost her spirits further, the hospital authorities had even considered the idea of showing her television so that she realised action was being taken against the culprits.
"We did think of it initially but then decided against it as it would have meant moving her from her bed," said a doctor in the hospital. Her parents are anxiously waiting outside the ICU, but doctors have not allowed the father to meet her and even the mother has met only twice to avoid infection.
The condition of the girl had marginally improved on Tuesday morning, and she had even started communicating with the doctors by writing small chits. 'Lift my leg', 'pain in my right leg', 'clean my throat, it's burning,' and 'have they been caught' were some of the notes written by her through the morning.
However, later during the second assessment, doctors found her condition had deteriorated.
"She needed more ventilatory support, her pulse rate is high at 130 (normal is between 70 and 80), her platelets have dropped to 48,000 (normal is between 1.4- 4 lakh) and her blood pressure has also dropped considerably, which indicates developing of the infection," said Dr Athani.
Doctors may perform another life-saving surgery on her to remove dead tissues, if required. "The surgery we performed on her was absolutely necessary to save her life and if need be, we may perform another one in coming days," said a surgeon.
"We are performing life-saving measures right now, and reconstruction surgeries will be performed after she has survived the life-threat," he added.
Sonia writes to Shinde and Sheila Dikshit, wants immediate action
Congress president Sonia Gandhi shot letters to home minister Sushilkumar Shinde and Delhi chief minister Sheila Dikshit after visiting Safdargjung Hospital for immediate action against the rapists.
In her letter to Sheila Dikshit, she said, "It's a shame that these incidents recur with painful regularity and that our daughters, sisters, mothers are unsafe in the capital city." She directed the chief minister to take "whatever steps are necessary to undertake community action, to strengthen law and order, and to step up vigilance to protect women."
To the home minister, she wrote, "It's a shame for all of us who are responsible for security of our cities. This monstrous crime deserves not only universal condemnation but also the government's most urgent attention. It is imperative that the police and other agencies concerned are sensitise to the danger our daughters, sisters, mothers face every day. The security agencies must be motivated, trained and equipped to deal with this menace.
Congress chief Sonia Gandhi on Tuesday night visited Safdarjung Hospital to inquire about the condition of the 23-year-old gang-rape victim and asked the government to take the strictest possible measures to ensure that there is no recurrence of such a barbaric incident that has shaken the country.
Gandhi was at the hospital here for about 15-20 minutes during which she inquired about the condition of the girl from the doctors and met her parents, according to Congress general secretary Janardan Dwivedi.
The doctors told Gandhi that the girl was in a critical state, he said.
According to doctors, the condition of the para-medical student, who was gang-raped and brutally assaulted by a group of men in a moving bus here on Sunday, had deteriorated in the evening after which she was put on "full-time ventilator support".
Four of the six accused were arrested and sent to police custody for five days on Tuesday. Two are still missing and the police are reportedly searching for them in Rajasthan and Bihar.
The police have added three more sections of Indian Penal Code against the accused.
The accused had decided to "punish" her for trying to stop them from attacking her male friend who was accompanying her, police sources said.
The men, including the bus driver Ram Singh, had taken out the bus for a joy ride on Sunday evening. They spotted the student and her friend at the Munirka bus stop in south Delhi and called out to them saying the bus was headed to Dwarka, where the woman lives.
The six men were apparently so confident they will not be caught that the assailants carried on with their routine chores the next day while one brought back the vehicle to his house.
But luck ran out for the men within 24 hours as police, who were aided by the description provided by the victims about the vehicle, zeroed in on them and even arresting one from Rajasthan where he was in hiding.
Just before raping the 23-year-old para-medical student in a moving bus on Sunday night and beating her male friend who tried to protect her, the gang of six men, two of them still absconding, looted a carpenter by providing him a lift in the bus.
Police investigators discovered that Singh has criminal records: He is wanted in an accident case. Plus, sources said, his elder brother, Suresh, was jailed after being convicted in a rape case six months ago.