The trial of four adult suspects accused of the fatal gang-rape of a student on a New Delhi bus in December will conclude on 10 September, the presiding judge Yogesh Khanna said Tuesday.

Dismissing pleas for more time by defence lawyers, the judge told the court: "You've delayed this trial far enough. My judgement will come on the 10th."

The first verdict in the case was delivered on Saturday in a juvenile court where a teenager, aged 17 at the time of the assault, was found guilty and sentenced to three years in a detention centre.

The four adult suspects face the death-penalty if convicted of the most serious charges against them which include murder, gang-rape and theft.

The "fast-track" court in the capital began hearings in February with the prosecution laying out evidence against the suspects, including DNA, witness statements and dying testimony from the victim.

The 23-year-old student was repeatedly raped and violated with an iron bar in a horrifying crime that brought anger about endemic sex crimes in India to the boil, sparking street protests and a toughening of sentences for rapists.

"I am grateful to your lordship for conducting this trial," Dayan Krishnan, special public prosecutor, told the court on Tuesday. "I am not so grateful to the defence team, which took almost 130 days on this."

"In my view, a just and speedy trial should not take so long," he added.

The four accused sat in the back row of the small court room, listening intently to proceedings.

After the judge announced the date of judgement, members of the prosecution team shook hands and congratulated each other.