Monks are not exempt from laws so it should not even be a question of should they be arrested. They broke the law in a disgusting fashion pure and simple. I have no idea even what the excuse could be to do such horrific acts. The Buddhists should be horrified.
If the Buddhist Temple is in fact involved in the black market for endangered tigers, they need to be shut down. Tigers require a large roaming area and trying to keep 147 tigers in one place is asking for trouble. While they may seem gentle enough for guests to interact with them, they are still wild animals and should be treated as such. The tigers should be protected and the Temple shut down for illegal activity.
One of the most important tenants of Buddhism is the concept of ahisma, which is, at its most basic level, nonviolence. The temple has proven to be unethical, but also to not represent the values of the Buddhist way of life. Animal trafficking itself is a terrible act, but the death of these baby tigers is especially heinous.
A Buddhist Temple is a religious place. Yeah, animal trafficking is horrible and it's shocking that they used the Temple for such a thing, but the Temple itself is still fine and can be used for normal religious practice even after this has happened. It seems like a waste to shut it down. Give it new ownership or something instead, get rid of the people in charge of the animal trafficking.