I can't presume to speak for Nirdesh Upadhyay, the father whose son the monkey's threw off the roof, but it if happened to my son, there wouldn't be very many monkeys in that neighborhood ... not living monkeys, at any rate.
Just capture the monkey that threw the kid over. Then hold him prisoner. Then every day capture more monkeys, and make the murderer monkey watch as you exterminate his race of monkeys everyday. Then kill him last.
I was thinking more along the lines of monkey target practice.
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