The retrial of 17 Hindus charged with murdering 14 people, 12 of them Muslims, in riots in 2002, is under way in the Indian city of Mumbai (Bombay).
The victims were burned alive inside the bakery
The victims were burned to death in a bakery in the western state of Gujarat, in violence that claimed 1,000 lives.
India's Supreme Court ordered a retrial after a Gujarat court acquitted the Hindu defendants.
Muslim and civil rights groups say witnesses were intimidated by police and some right-wing Hindu groups.
The victims were killed in what is known as the Best Bakery case - named after the bakery allegedly attacked by a mob of Hindus in the town of Baroda in Gujarat.
The accused have pleaded not guilty.
Twenty-one defendants were acquitted in the original trial in Gujarat. Four have since absconded and are being tried in absentia.
The BBC's Sanjeev Srivastava in Mumbai says elaborate security arrangements were in place inside and outside the court building with witnesses, lawyers and journalists all frisked.
The Gujarat riots of 2002 left about 1,000 people dead
The defendants sat quietly as the court spent most of the day examining a map of the Best Bakery.
Our correspondent says the judicial system in India is often slow and this could be a prolonged case.
The Supreme Court ordered that the retrial be moved out of Gujarat after accusing the state government of judicial failures.
A key witness admitted lying in court and not testifying against the accused. She said she had been threatened by senior figures in the local organisation of Gujarat's ruling right-wing Hindu Bharatiya Janata Party.
Several other prosecution witnesses also withdrew their evidence.
The retrial is the first step towards ensuring justice for the victims of the Gujarat riots, our correspondent reports.
The 2002 riots were sparked off after 58 people were killed when a train carrying Hindu activists was set ablaze by a suspected Muslim mob near the town of Godhra.
Subsequent riots in Gujarat left more than 1,000 people, mostly Muslims, dead.