Calling it a "premeditated" and "brutal" crime, a judge Tuesday convicted four men for the Dec 16, 2012 gang rape and murder of a 23-year-old physiotherapy intern in a case that jolted the nation and made global headlines.

"She was gang raped by six persons one by one and...iron rod and hands were inserted into the abdominal cavity...(and a) major part of her intestine was pulled out from the body. This aspect shows the severity of injuries caused to the victim," said Additional Sessions Judge Yogesh Khanna.

"I convict all the accused persons for gang rape, murder of the helpless victim, attempt to kill complainant (victim's male friend), conspiracy, common intention, destruction of evidence, kidnapping...," the judge announced.

He said the injuries on her person, including "18 injuries" to her internal organs, inflicted by the accused were "dangerous" and "sufficient....to cause death."

Convicts Mukesh, Pawan Gupta, Vinay Sharma and Akshay Thakur, who face a maximum of death penalty, are likely to be sentenced on Wednesday.

The four convicts, who have been in judicial custody since their arrest soon after the crime, were present in the court when the verdict was pronounced. Vinay Sharma cried on hearing the judgment.

The gang rape occurred after the woman and her male companion boarded the bus in Munirka in south Delhi to return home after watching a movie.

The six attackers in the bus threw both the woman and her male companion out of the vehicle -- without clothes -- on the street in the cold December night after committing the crime, police said.

The woman died of her injuries Dec 29 at Singapore's Mount Elizabeth Hospital, where she was airlifted for specialised treatment.

While one of the six accused was found dead in a cell in Delhi's Tihar Jail, a juvenile involved in the crime was Aug 31 sent by the Juvenile Justice Board to a reform home for three years after it concluded that he was involved in rape and murder.

The incident sparked nationwide protests and nudged the central government into enacting a stringent anti-rape law.

The court said the convicts' act of inserting rods into the body of the victim was done "intentionally" to kill her.

"The act of insertion of rods and pulling out the internal organs after committing the gang rape in no manner can be seen as acts done only to facilitate the commission of gang rape," the court said.

The injuries were caused in a "brutal manner" and the death was also not accidental, the court said in a judgment which runs into 237 pages.

Judge Khanna said the nature of the convicts' acts suggested that none of these were impulsive but "clearly establishes the acts as being premeditated".

The manner in which rod were used and injury on the body of the victim was inflicted ruled out the possibility that the accused brought the rod "to overpower the victim", who subsequently died of her grave injuries.

"The victim died due to injuries inflicted by the accused while committing various offences with the victim inside the moving bus on Dec 16, 2012. Such injuries have been described by the doctors as dangerous, extremely bad for definite repair, sufficient in the ordinary course to cause death," the court said.

"Multiple severe injuries to alimentary canal can by no stretch of the imagination be the outcome of commission of the offence of gang rape by six persons," the court said.

The judge said that force was used on the victim while torturing her and that caused severe injuries to her, from which she ultimately died.

The rod caused as many as "18 internal injuries to several organs" and the cause of death in the case was the direct consequence of the multiple injuries sustained by her, the court said.

The judge said that the evidence of complainant (victim's male friend), who was in the bus, was of "vital importance" for deciding the case.