Cases running in India. Even in US some cases were filed earlier. This are some old threads:Why wait for so many years? Not saying that Amitabh is a saint.
US court to hear 1984 anti-Sikh riots case on March 29
Amitabh Bachhan's Role in 1984 anti Sikh riots
US court issues summons to Sonia Gandhi in 1984 anti-Sikh riots case
U.S. court to hear anti-Sikh riots case on May 1