The missing wife of a man killed by police in the western Indian state of Gujarat in 2005 was also killed and her body was burnt, the state has admitted.
Police said Mr Sheikh was plotting to assassinate Mr Modi (above)
Gujarat government lawyer KTS Tulsi told the Supreme Court that they were trying to find Kausar Bi's remains.
Last week, three top policemen were charged with the murder of the husband, Sohrabuddin Sheikh, a Muslim civilian.
They are alleged to have attempted to cover up the killing by claiming he belonged to an Islamic militant group.
Mr Tulsi submitted a sealed report to the Supreme Court on the case on Monday and the judge said he would respond on Tuesday.
Kausar Bi had been travelling with her husband by bus when they were taken away by the Gujarat police.
She has not been seen since her husband was allegedly shot dead in a "staged encounter".
At the time, police claimed Mr Sheikh belonged to the banned Kashmiri militant group, Lashkar-e-Toiba, and was plotting to assassinate the Gujarat Chief Minister Narendra Modi.
In March, the state police admitted - at a hearing of the Supreme Court - that Mr Sheikh was killed in a staged gun-battle.
On Friday, the state government told the court that Kausar Bi may have been killed too.
The revelation came after Mr Sheikh's brother, Rubabbudin Sheikh, filed a petition in the court demanding an inquiry into the killings by India's federal police, the Central Bureau of Investigation (CBI).
He also asked the judge to direct the Gujarat government to produce Kausar Bi in court.
Gujarat has been heavily criticised for the treatment of its religious minorities.
According to official figures, more than 1,000 people, mostly Muslims, were killed during the riots that broke out after nearly 60 Hindus were killed when a train was set on fire in Godhra town, allegedly by a Muslim mob, five years ago.
The state administration was accused of not doing enough to stop the riots.
Security forces in India have on occasion admitted to extra-judicial killings - described by the local media as "fake encounters" - in which they had at first said they had killed militants after coming under gunfire.
Last year, the US-based Human Rights Watch released a report which said the Indian army had admitted to extra-judicial killings of militants in Indian-administered Kashmir.
In February, Kashmir police said DNA tests confirmed that a supposed Pakistani militant reportedly killed in a gun battle was a local civilian.
Police there are also looking into four other reported extra-judicial killings.
Soldiers are also accused of gross human rights violations in the north-eastern state of Manipur and the people there have been holding protests for years demanding an end to the special powers enjoyed by the armed forces.