Nearly 1,600 cases relating to the 2002 religious riots in the Indian state of Gujarat are to be reinvestigated, police say.
More than 40 police officials are also to be probed for allegedly failing to adequately investigate the cases.
More than 1,000 people, mostly Muslims, died in the riots.
The violence broke out after 60 Hindus were killed when a train was attacked in the town of Godhra, allegedly by a Muslim mob.
The Gujarat government has been criticised for its handling of the riots and its alleged failure to provide justice to the victims.
The decision to reopen the cases comes after a Supreme Court order in 2004 to review more than 2,000 cases that had been closed by the police.
The court ordered the Gujarat government to give it quarterly reports on the progress of the cases.
"This is the first time that we will initiate a departmental inquiry against investigating officers who failed to carry on the probe of riot cases," Gujarat state police chief AK Bhargava told Reuters.
He said in the past 18 months, 640 accused had been arrested and 13 new cases registered.
Forty cases have, however, been closed for lack of evidence.
In December a special court sentenced 11 people to life imprisonment for killing 11 Muslims during the 2002 riots.
Only a handful of cases have been brought to court following the riots. Fewer still have ended in convictions.
The riots were among the worst in India since partition in 1947.
They were sparked when the Sabarmati Express, carrying Hindu pilgrims returning from the disputed holy site at Ayodhya, was attacked.
How the blaze began is still not clear.
An interim inquiry conducted by the rail ministry concluded that the fire was an accident, although this view is being challenged by many.
A judicial inquiry into the riots has yet to report