By Geeta Pandey
BBC News, Delhi
Ms Mattoo was found strangled in her Delhi flat
A young and lively Delhi law student is raped and murdered in her house.
Before her murder, she complains to the Delhi police that she is being stalked and harassed by a fellow student, Santosh Singh.
After her murder, witnesses say Singh was seen near the scene at the time of the crime.
Following a badly botched up trial that went on for three years, Singh is acquitted by a trial court in 1999 for lack of evidence.
But while acquitting Singh, the judge lashed out at the prosecution.
He said the investigating agency, the Central Bureau of Investigation, had manipulated evidence and ignored proper procedures.
He said he knew the defendant was guilty but was obliged to acquit him.
To salvage its image, the CBI filed an appeal challenging the acquittal in April 2000.
But the case files lay forgotten, gathering dust.
'Error of judgement'
For six long years, not one single hearing was held.
Ex-chief justice Khare wants judges to be proactive
But in July this year, it all changed. The Delhi High Court ordered a retrial and put the case on fast-track, holding hearings three times a week.
After only 12 days of hearings, a guilty verdict has been announced.
Santosh Singh has been convicted for rape and murder and the judge has threatened that the punishment will be harsh - the death penalty or a life sentence.
It has been a case of justice delayed, but not justice denied.
And the decision is being hailed by most.
"I am very pleased. Justice has been done," says the former chief justice of India, VN Khare.
"There was so much circumstantial evidence in the case, the accused should not have been acquitted. Priyadarshini Mattoo had lodged complaints with the police, Singh was seen at the scene of the crime before and after the incident, it was an error of judgement," he says.
Indu Jalali, a friend of the victim, says: "Our faith in the judiciary has been restored. The court has sent out a message that no one can get away with wrong-doing, however powerful and well-connected they may be."
It took years to bring Santosh Singh to justice
So what prompted the fast-tracking of the case?
One element was a tireless campaign by activists and friends of Mattoo's who formed a group called "justice for Priyadarshini".
They launched their campaign with a candle-light procession from the sprawling lawns of India Gate.
Thousands of mobile text messages were sent to build public opinion in support of the campaign.
And a sustained campaign was also run by the media, with television channels debating the health of India's criminal jurisprudence.
Newspapers devoted reams to finding loopholes in the prosecution's case, which had led to Singh's acquittal.
And most say if it hadn't been for the media spotlight, the case files would probably still be gathering dust.
But some legal experts say media campaigns in criminal cases may be setting a very dangerous trend.
"The media is putting tremendous pressure on the courts," says criminal defence lawyer Rebecca John.
"I'm not saying the judges in the Mattoo trial case were influenced, but the judiciary is bound to err at some stage if you put it under this kind of scrutiny."
Ms John says the media is selective in its campaigns; it builds them around "pretty, upper middle-class, urban women" - while thousands of similar cases in rural areas and involving poor people go unreported.
Well-known lawyer Indira Jaisingh says "the media does play a role in advertising and giving exposure to a case and that may motivate a court to put a case on the fast-track".
But, she adds: "It's unlikely that what's written in the media will influence the judgement. There the judges go by evidence."
But both Justice Khare and Ms Jalali single out the media for its unrelenting support during the campaign to punish Mattoo's killer.
"The credit goes to the media. They took up the case and kept the spotlight on, otherwise it would have continued to languish in the files," says Ms Jalali.
Earlier this year, media attention and public pressure also resulted in the re-opening of another case, that of murdered Delhi model Jessica Lal.
Several men accused over the killing were acquitted, resulting in a huge public outcry.
The two cases have highlighted the growing discontent in India at what many say is its ineffective legal system where high-profile perpetrators are almost never punished.
Justice Khare says, in such cases, media activism may not be a bad thing all the time.
His advice to judges trying cases like these is to be more proactive: "If you feel strongly that someone has committed a crime, you must go by the circumstantial evidence."