It took over 15 minutes for the zoo keepers to do anything, by which time the man was killed.

https://www.youtube.com/watch?v=X19UZbM4Sj4

Very sad.

why the heck the staffs in the zoo never used tranquilizer or guns to kill this animal? A human life is way important than that tiger, ain't it? what kinda moat they built where people fall, undeveloped countries

"A human life is way important than that tiger, ain't it?"
says who?
In a country of 1.3 billion that is destroying the earth and its resources, you really think that? Irony is Bengal tiger is a native of India and their population is dwindling every year while these curry smelling species are multiply more vigorously than any animals, is that a justifiable reason to say? FYI, bengal tiger population is only in few thousands - indian people 1.3 billion and counting. Valuing human life so blindly is the cause of over-population in these parts of the world.
This is simply a matter of inefficient zoo management. Many question arises here. How the hell did the guy get in there? Where was the security?
But the underlying fact and the truth still remains, this was NOT the tiger's fault and he/she should NOT be punished in way. It is as clear as the day light. Sad but true.

There's some truth to Divorceguy's point, although I also agree with Vhotee.
Zoos like this should have guards with tranquilizers ready to be deployed. The tiger shouldn't be shot but tranquilizer or tear-gas could've been used. The report says that the zoo was not equipped with such deterrents. Also, it's not very clear whether the fence was built adequately.

A tiger killed a man and I remembered this GBS' quote

“When a man wants to murder a tiger, he calls it sport; when the tiger wants to murder him, he calls it ferocity. The distinction between crime and justice is no greater.”

But I agree with Kiddo, they should have some plan to prevent accident like this. Shame on Zoo management.