Anonymous leaking the information or personal identities of criminals are good. It helps them catch dangerous criminals such as criminals who are charged for murder. People are scared of the criminals and Anonymous help them catch them. Even though hacking is a crime, the government can make exceptions. Who would like dangerous criminals roaming the streets of their neighborhood.
Anonymous people shouldn't be trying to track down criminals through means if their own hacking. This is the job of paid workers, whose job is to track criminal activity through the web. These 'anonymous' people should be leaving it to the professionals to catch people in this method.
Not only that, but if the police get an anonymous message, saying so and so is a criminal, and they did such and such, don't think that the police will be taking it as immediate fact. There would definitely be superstitions of it being a prank, or even a criminal trying to pull something.
Some criminals has committed crimes related to hacking. These criminals are better than most of the cyber police. They have more experience than paid workers. If police just gets a message from the Anonymous, they sure will just think that it is a prank, but the Anonymous are going to give them evidences. The Anonymous leaked KKK members' identities. History stated that Ku Klux Klan is "a vehicle for white southern resistance to the Republican Party"s Reconstruction-era policies aimed at establishing political and economic equality for blacks." They commit crimes to kill or beat up other races which are not Whites. The Anonymous stated, "We removed several names from our list for further investigation. We would rather have a smaller, accurate list that we are comfortable with." They removed some names from the list of names of KKK members to find more evidences and put together. Police or other investigation organizations will appreciate helps from the Anonymous. They will believe the Anonymous' messages with evidences.
While its true that most criminals that are related to cyber hacking have lots of skill and experience with what they do, don't confuse yourself by thinking that they have more skill than the cyber police. A relative of mine works with the Canadian government to track down hackers, such as the ones we are discussing. He has gone through many years of computer science and programs in university to get his position. He works with several other workers, each of them have tracked down several cyber criminals, and they certainly have more skill and experience than most cyber criminals out there.
If someone anonymous, like the one you told us about, wants to reveal information about cyber criminals, and their work is not only useful, but accurate as well, than I believe to avoid suspicion and confusion, this person should not give their findings without an identification for themselves. These people should even be running for positions similar to that of my relative. This way, they will not only be able to share their findings, but unlike the option of working under an unknown cover, they will also get the chance to discuss further with the police as to the details of the crime, that would be more difficult to make known when anonymous.