Investigation takes time, effort and money. Its why the police is a group of people being paid to do that work. No one expect the police force to be made out of voluntaries. Why do then suddenly people expect system administrators to do police work for free?
How common is it that people go to the local police station in an afternoon and offered to do some work with no expectation of some kind of salary?
System administrators are not people that work for free. They expect to get paid like everyone else. They also expect to be able to decide what work they accept, and which ones they do not (ie, they are not slaves). Some do investigations for the police without getting any payment because they feel they want to perform some civil duty to do so, but the above comment imply that they must do so. That is wrong. System administrators should not be forced labor for the police.
If there is investigation to do, call the police, pay your taxes (so the police get paid), and let the system work as intended without putting forced labor onto the system administrators of the world. If you dislike a service because its used by criminals (like say, gmail which is abused by spammers), it still the police you should call and not the system administrators.