What do you think should be done with beast Moninder Singh of infamous Nithari killings?

I think he should be tried, and, if found guilty, sentenced according to the law. That is what happens in a decent society. The guilt of the suspect has to be proven first. It is a sign of vigilanteism and lawlessness for you to be asking this loaded question. "What ... should be done" indicates that you already consider him guilty, and want him to receive some form of punishment. "Beast" indicates your emotive outrage, and decisions made on an emotive basis are rarely good ones. Calm down, and await the due process of the law.