You have to think that what makes a journalist is his integrity. Meaning that if you snitch on people you interview, you won’t have another. Then, I also wouldn’t be surprised that the criminals use means not to be snitched about (maybe dig some dirt on the journalist, not using their real names or even wearing masks, meeting at hotels …). Also, even if it seems simple, you may need weeks of trying to get in touch with someone behind one interview.
As a journalist you can also try and interview criminals that got caught. This way, you don’t have to bother about anonymity and what the criminal will tell, he surely already told the authorities so that it’s not a secret anymore.
As for the criminals, I guess that a documentary about them is free and legal publicity, wether it is used to make people scared or try and sell their lifestyle (or make people back away from it depending on who you’re speaking with). And it is also an acnowledgement of their importance since you don’t undertake the making of a documentary (which needs from a few weeks to years sometimes) for something or someone that isn’t worth being talked about
Edit : typo
I think they do it for a few reasons:
Publicity: They want people to know they exist.
Legitimacy: They aren’t just a ragtag group of thugs, they are an organization with some level of professionalism that is important enough to be interviewed.
The human side: They want to show that they are people too. This might garner some sympathy from the public.
They also ensure the leaking is kept to a minimum. Sometimes they will take the interviewer to an unknown location. They closely monitor what is recorded, etc.
if you are a journalist that does this kind of material and proceed to then sell out the people you just interviewed you can be assured that no one in that field will ever talk to you again, assuming you dont end up facing blowback from the people you just screwed over.
you can also be assured that even if you outlive this you likely just lost your job and no one in the business will want to hire you as you are too much of a liability.
ofc there are exceptions ie: when there is a legitimate reason ot believe lives are in immediate danger from what you just witnessed but that rough and these organization rent THAT lax around strangers.
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