Although I don't like Khushwant Singh very much, but read this :
http://www.outlookindia.com/full.asp?fodname=20041115&fname=Sikh+%28F%29&sid=1
Oh, That Other Hindu Riot Of Passage
The assassins of Mrs Gandhi were hanged within four years, while 20 years later, the killers of 10,000 Sikhs...