As he recalls the attack that killed his best friend and left him grievously wounded, the young IT operator still can't fathom the depravity they encountered after a night out at a Delhi shopping mall.

"I never imagined that one human being could treat another so badly," said the 28-year-old about the fatal gang rape of his female companion on December 16.

"The rapists injured my friend in the most shocking ways while they beat me with a metal bar and dumped us near a highway."

"They wanted us to die. Now, I want them to die and she also wanted them to die... She wanted them to be set on fire."

The young man, who cannot be named to prevent identification of the victim, visited his friend twice at a Delhi hospital before she was airlifted to Singapore by the Indian government for further treatment.

"She was in enormous pain but wanted to talk to me and her family. She would recall the incident and get very angry... We would quickly change the subject."

"I would ask her about the new clothes she bought with me and make plans about things we would do when she recovered. Those plans died with her."

In an interview with AFP ahead of Tuesday's verdict, which saw four men convicted of murder and gang rape, he said how he is wracked by guilt for being unable to protect his 23-year-old friend as they made their way home from the cinema.

The pair had spent the Sunday evening watching 'Life of Pi' and were trying to flag down an autorickshaw when a bus pulled up.

It was only after boarding that they realised it was no ordinary bus and that their fellow passengers were in fact a group of drunken joyriders who would rob them before conducting a sickening assault.

Nearly unconscious after being savagely beaten, he could do nothing but watch as his friend was repeatedly raped and then violated with an iron rod.

The victim's intestinal injuries were so horrific that they led to her death in a Singapore hospital where she suffered multiple organ failure on December 29.

Severe injuries left him unable to attend his friend's funeral. The accused had broken his leg, stripped him and kicked him out of a moving bus along with the victim.

But determined that her attackers would face justice, he was the first of up to 80 witnesses to reveal before the court what he had experienced and seen on December 16.

The trial may be over but the young man, who moved to Delhi in 2006 from the northern state of Uttar Pradesh, is still struggling both physically and psychologically.

He resumed work in May this year and worships a Hindu god every evening.

Sometimes he goes to the cinema alone but his friend's fate is never far from his mind.

"I could talk to her about anything, tease her and even share my coffee with her. Companionship and friendship meant being with her.

"She was cool, funny, mischievous had a great presence of mind. She could make anyone smile and maybe that is the reason why every Indian was angry and sad when she died," he said.

"Her case made everyone feel guilty... society could not protect her.

"For me, I lost a friend... The guilt will always remain. The only good thing would be if we ensure that such cases do not happen ever again."

He has been critical of the police for failing to be sensitive to his mental condition and deplored the apathy of the passers-by who did little to help at the end of their nearly hour-long ordeal.

"I wake up and the first thought that comes to my mind is always about the attack.

"Sometimes I think about my friend, sometimes about the rapists. It sends shivers down my spine."