(Orignally this was a reply to a reply of this comment that apparently got deleted.)

What if while arriving on scene to a burglary there is body camera footage from an officer that appears to show someone running off and away from the scene carrying [whatever was stolen] and from that footage one could possibly conclude that the personal doesn't look like the person the police decided to accuse and prosecute. This could be exculpatory evidence and help clear you of the charges. (Obviously the prosecutor is suppose to let the defendent and court know of any known exculpatory evidence, but what if the police choose to withhold it from the prosecutor/court or don't think anything of the footage? )

What if it isn't going to be used against but could be exculpatory?

Of course, it's illegal for them to withhold any exculpatory evidence.

If its not public, you have minimal chance of discovering it if it isn't provided, so while it is illegal for them to withhold it, you'll never know it existed and was withheld unless someone who does know of it -- almost certainly the police themselves, or the person shown in it (quite possibly, the real criminal, who would be revealing their own identity by coming forward) -- actively reveals it. So, illegal or not, it makes it much easier for them to get away with concealing exculpatory evidence.