Yes, quite often the makers stage scenes in order to basically setup the subject of their interview as well. We now know that Martin Bashir's most famous interviews was done by lying to their famous subjects in order to lure them in too. Footage has also emerged of Bashir fawning to their faces whilst saying something completely different in the editing room.
And so on it goes for documentaries other than "Death On The Rock".
Problem is, once these manipulated, skewed documentaries are broadcast many people take them at face value, believe them and NEVER go beyond them to actual court documents. Evidently, this is too much effort for most people.
Inevitably, this also means that not every opinion is valid or equal. Indeed, as you point out such documentaries CAN prejudice criminal proceedings as well as investigations.
Very often, you really do have to wade through tons of propaganda in order to get at the established facts. Unfortunately, the fact media publications ARE businesses FIRST and FOREMOST also means that established facts are easily buried. The aim is to sell enough copies or pull in enough viewers as this means money.
Media publications are reluctant to acknowledge when they were wrong or their methods were unethical. At most, you'll see a TINY retraction buried on page 13 or so. Maybe a financial settlement. But nothing explicit in case it damages their own credibility with their target audience.
Terrorist groups that understand the value of propaganda also know most people cannot detect bias if it hit them on the head. It easily plays into their hands.
Indeed, it was naive for anyone to think the Leveson Enquiry into media hacking would fundamentally change things. It hasn't.
There is STILL no substitute for letting criminal proceedings follow due process. Unfortunately, many argue against this by using a logical fallacy called Circular Reasoning amongst others.
If we are to automatically believe anyone who makes a claim, then people such as Carmen Proetta would be believed OVER actual evidence and established facts. It would mean the allegation the SAS shot the PIRA 3 in cold blood on the ground with one soldier with his foot on Savage's neck would stand.
The reality is, of course, rather different as that actually didn't happen. Pathologist's report disproved those allegations, for example.
It is dangerous to believe a, b and c because of allegations made by x, y and z. Allegations and the case against MUST stand on its own feet with corroborating evidence.
A documentary isn't necessarily evidence or reliable evidence as shown by the blatant lies in "Death On The Rock".
Facts aren't about feelings either. This would be falling into the Affective Logical Fallacy, for one.
With Russell Brand, let the authorities do their jobs without undue external prejudicial Interference.