In my opinion, the Dalai Lama has to take some responsibility also. He probably has been covering people up over the years and these people think the Dalai Lama will continue to do that for them. If the Dalai Lama does something different, ie to openly condemn the behaviour of these criminals, no one will dare to use his name anymore.
The Dalai Lama is not above the law, he has to follow the rules as well. Just because he is a reincarnated lama, it does not mean he can do anything that he wants and everyone has to give way to him. It might be the case in the old Tibet but in the modern world, everyone has to abide by the law.
The reason the Tibetan leadership fails in so many things is that they still have the mentality of the older days, thinking they are above all. Even though they say they are democratic but they don't really understand what it means. There is still favouritism and nepotism in the Tibetan leadership.