A senior politician from India's Congress party has been jailed for life in the most significant conviction to date over the 1984 anti-Sikh riots.
Sajjan Kumar, who was an MP at the time, was found guilty of inciting crowds to kill Sikhs.
In a scathing verdict, the Delhi high court judges said the accused evaded justice due to "political patronage".
More than 3,000 Sikhs were killed following the assassination of then PM Indira Gandhi by her Sikh bodyguards.
They were angry at her decision to send the army into the Golden Temple - Sikhism's holiest shrine - to flush out militants earlier in the year.
The killing of Mrs Gandhi, who belonged to the Congress - now India's main opposition party- saw mobs attack and murder members of the Sikh community across the country. The worst violence took place in the capital, Delhi, where more than 2,700 Sikhs are believed to have died.
For 34 years, high-profile politicians accused of involvement in the anti-Sikh riots had evaded justice - on Monday this changed with Sajjan Kumar's conviction.
However his lawyer told journalists that he would appeal against the verdict in the Supreme Court.
There are a number of cases against Kumar relating to the riots - Monday's verdict is specifically over the killing of a family of five in Delhi.
Kumar, 73, had been previously acquitted by a lower court for his role in the riots, but the verdict was challenged by the country's top investigative agency which said he had been involved in a conspiracy of "terrifying proportions" with the police.
Jagdish Kaur, whose son and husband were among five family members brutally killed, described the verdict as "a little balm applied after a long time to our scars".
"At least one high-profile accused will now go to jail," she said.
Nirpreet Kaur, another victim whose father was burnt alive by mobs before her eyes, wept as she thanked the court for delivering justice after 34 years. Her case remains in the court system.
Ms Kaur told BBC Punjabi's Sarbjit Dhaliwal she was happy that Kumar had received a life sentence because a "death penalty would have meant he would have died in a moment, but now he will suffer".
Kumar was convicted after several eyewitnesses testified against him for inciting mobs in Delhi's Sultanpuri area.
One witness said she had seen him addressing a crowd, telling them that Sikhs had killed "his mother" - a reference to Mrs Gandhi.
Delhi high court Judges S Muralidhar and Vinod Goel found Kumar guilty of "criminal conspiracy, promoting enmity and acts against communal harmony" and ordered him not to leave the city and surrender by 31 December.
"In the summer of 1947, hundreds of thousands of civilians were massacred during the Partition of India... Thirty seven years later, India was witness to another enormous human tragedy... A majority of the perpetrators of these horrific mass crimes, enjoyed political patronage and escaped trial," the judges said.
"This court is of the view that the mass killings of Sikhs in Delhi and elsewhere in November 1984 were, in fact, 'crimes against humanity'. They will continue to shock the collective conscience of society for a long time to come," they added.
Finance minister Arun Jaitley welcomed the verdict. However, opposition leader and Congress party president Rahul Gandhi is yet to make a statement.
Sajjan Kumar’s conviction by the Delhi High Court is a delayed vindication of Justice. The Congress and the Gandhi family legacy will continue to pay for the sins of 1984 riots.— Arun Jaitley (@arunjaitley) December 17, 2018
Following the verdict, Sajjan Kumar, Delhi high court and #1984SikhGenocide were trending on Twitter in India with thousands of people tweeting about the case, including Delhi Chief Minister Arvind Kejriwal.
I welcome Delhi High Court verdict convicting Sajjan Kumar in 1984 riots case.— Arvind Kejriwal (@ArvindKejriwal) December 17, 2018
It has been a very long n painful wait for innocent victims who were murdered by those in power.
Nobody involved in any riot should be allowed to escape no matter how powerful the individual maybe.
Manjinder Singh Sirsa, Shiromani Akali Dal on conviction of Sajjan Kumar in 1984 anti-Sikh riots case: We thank the court for giving us justice. Our fight will continue till Sajjan Kumar & Jagdish Tytler get a death sentence & Gandhi family is dragged to the court & put in jail. pic.twitter.com/TtfEXn4Qiz— ANI (@ANI) December 17, 2018
Apart from Kumar, several other high-profile Congress politicians are accused of involvement in the violence.
Among them is Kamal Nath, who was sworn in as the chief minister of Madhya Pradesh state on Monday. Jagdish Tytler, who was the minister of state for overseas Indian affairs at the time, is also one of the main accused in a number of cases. Both deny any involvement.
Sikhs are a religious minority in India and at 21 million, they make up close to 2% of the population. There are significant Sikh communities in Canada, the UK, US and Australia.
'No closure on a dark chapter'
Atul Sangar, Editor, BBC Punjabi
The conviction and life imprisonment awarded to Kumar, along with jail terms awarded to five others, comes as some solace to the Sikh community, but will not act as a closure on that dark chapter.
Thousands of Sikhs, whose family members were killed by rampaging mobs in November 1984, have welcomed this judgement. However, their deep sense of anguish and hurt over the massacre and then this long fight for justice is unlikely to go away easily.
There are other cases pending in the courts, including one against former Congress minister Jagdish Tytler, who denies any hand in anti-Sikh violence.
Though more than 400 accused have been sentenced by courts in these cases, victims have repeatedly complained that adequate steps were never taken to bring high-profile Congress leaders to justice.