I'd really like your evidence for that because you seem to put the police/offical statements as fact See this article that shows officers don't lie less than the public: http://digitalcommons.pace.edu/cgi/viewcontent.cgi?article=1527&context=lawfaculty
I am not suggesting that another group started the bridge fires, to do so would be speculation since I have no information on the matter that I deem trustworthy from a reliable source. I agree with your assessment that it is likely that it was the protestors, since I really can't imagine what law enforcement would stand to gain by doing so, but again I can't know that. Unless it was to give the appearance that the protestors were rowdier and more disorderly, fortifying the premise on which to crack down on them? The void of information is incredible.
There is a derth of information; though some is less reliable than others.
Actually, in the last few posts I have posted photographic evidence, an independent reporter's account (accompanied by video footage), local news coverage and national news media coverage. I'm not sure how many more sources I should explore? I've never stated a police report as 'fact', and have clearly admitted there is bias on both sides of the issue, which is why I offer several sources. No single source is intended to be all-encompassing; there is so much information out there on the subject it would be silly to take only one and assume that it is fully complete.
If you're hung up on the word 'fact', then that's a semantic argument that is not helpful in supporting the rights of people to be civilly disobedient. I can't prove for a 'fact' that a specific protester lit cars on fire at a specific time; it is not my intention to do so. The cars could have driven themselves onto the bridge before spontaneously combusting. The police could have stolen these cars, lit them on fire, and then rode through town arresting random people for the crime because their alien overlords told them to. I mean, we can't prove for a 'fact' that this didn't happen. Really, we can't 'know' that this didn't happen.
But it can be stated that the most likely scenario, based on many eye witness accounts, and not refuted by anyone who was there, is that protesters built barricades and lit the cars on fire on the bridge. I mean, the evidence clearly moves the discussion far past the level of 'speculation.' More photographic evidence here
Actually your own post refuted the statements. Protesters said they lit fires after being attacked water cannons in freezing temps:http://www.nbcnews.com/storyline/dakota-pipeline-protests/dakota-pipeline-protesters-authorities-clash-temperatures-drop-n686581
You might not be as careful with a fire if you have soaked by water in temperatures as low as 23 degrees.
Now I am not saying, AGAIN, as I did on BOTH the 30th and 31st, that it is not likely that some members of the protesters used this as an opportunity to be violent and may have intentionally lit cars on fire. However, nothing you posted was evidence of that other than statements by police. The protesters have another side, saying they were trying to combat hypothermia after they were soaked by water in temperatures as low as 23 degrees. Neither the police nor the protesters are less bias or less likely to be lying.
You showed a picture of fire, no evidence of who or why. You posted a "news journalist" who has history of lying. Maybe if you actually posted someone without a history of lying or actual evidence, I would not be arguing. If you want someone to believe you, you need facts not supposition. Because when you look at supposition, I ask, who in benefiting from it and right now, it is not protesters. I also ask why the police have arrested journalists so that less biased information could come out and not just be from their statements? Who is benefiting from that?
Also, if you look at the news article I posted, the authorities whose statements you are taking as proof of action stated "Sheriff's spokesman Rob Keller told NBC News that no water cannon were deployed and that water was sprayed from a fire truck to control fires as they were being set by activists. However, video posted to Facebook by activists clearly showed authorities spray a continuous stream of water over demonstrators in areas where there were no fires." So please tell me why you seem to think their statements are actual proof?