What is more surprising in this news is not that the government was able to trace these transactions even after the police officer's efforts to eliminate the trace (I suppose that he made a mistake at some point) but the fact that the delinquent was a policeman.
If you leave traces before using mixers or after using mixers, you are visible by governments and they will find you, that's it. Privacy and anonymity are hard to gain as it is not achieved by a single action and moment but a long history of your actions over a very long time. It's like security, as if you have a hole on a very long wall of security, it can be exploited and a whole wall can collapse.
Similarly, if you left traces somewhere, other careful actions before or later that can not help you gaining complete privacy and anonymity.
Considering the fact that he had used a mixer to try and loot the funds but still got caught. That would conclude that his past actions were used to trace it back to him. Many people might feel that just by sending funds through mixers makes you invincible.. I'm still not surprised that he got caught and he should be.. these are the kind of people that gives privacy a bad image. If he wasn't caught, it would have added to the negative conclusion that privacy tools are bad.
Maybe it's because of the country I'm from but many I'm surprised someone is shocked that a police officer could be a thief.
Lol literally from a country where everyone including the authority is a criminal, this kinds of stories is not going to a surprise. Though in some countries it's same but they do it in the dark so it doesn't stain their images..