Krishna, in theory what you say is right. But in India every issue gets politicized.
If Modi (or anybody for that matter) arrests any Muslim in relation to the to the killings of Hindus or terrorism, all hell will break loose. First psuedos will cry attrocities against minorities and then taking a que from the psuedos, Jihadis will wage Jihad. The central govt will move to dismiss the state govt now that we have a rubber stamp for the President. The media and commies will immediately start round the clock comdemnation.
The riots were not the result of a single incident, but they were the result of an accumulation of pent up anger of the majority community.